diff --git a/sub/subClashService.go b/sub/subClashService.go
index c0871a89..a138faec 100644
--- a/sub/subClashService.go
+++ b/sub/subClashService.go
@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"maps"
 	"strings"
+	"time"
 
 	"github.com/goccy/go-json"
 	yaml "github.com/goccy/go-yaml"
@@ -63,12 +64,13 @@ func (s *SubClashService) GetClash(subId string, host string) (string, string, e
 		return "", "", nil
 	}
 
+	now := time.Now().UnixMilli()
 	for index, clientTraffic := range clientTraffics {
 		if index == 0 {
 			traffic.Up = clientTraffic.Up
 			traffic.Down = clientTraffic.Down
 			traffic.Total = clientTraffic.Total
-			traffic.ExpiryTime = subscriptionExpiryFromClient(clientTraffic.ExpiryTime)
+			traffic.ExpiryTime = subscriptionExpiryFromClient(now, clientTraffic.ExpiryTime)
 		} else {
 			traffic.Up += clientTraffic.Up
 			traffic.Down += clientTraffic.Down
@@ -77,7 +79,7 @@ func (s *SubClashService) GetClash(subId string, host string) (string, string, e
 			} else {
 				traffic.Total += clientTraffic.Total
 			}
-			normalized := subscriptionExpiryFromClient(clientTraffic.ExpiryTime)
+			normalized := subscriptionExpiryFromClient(now, clientTraffic.ExpiryTime)
 			if normalized != traffic.ExpiryTime {
 				traffic.ExpiryTime = 0
 			}
diff --git a/sub/subJsonService.go b/sub/subJsonService.go
index 29dbd987..e26b60ea 100644
--- a/sub/subJsonService.go
+++ b/sub/subJsonService.go
@@ -6,6 +6,7 @@ import (
 	"fmt"
 	"maps"
 	"strings"
+	"time"
 
 	"github.com/mhsanaei/3x-ui/v3/database/model"
 	"github.com/mhsanaei/3x-ui/v3/logger"
@@ -125,12 +126,13 @@ func (s *SubJsonService) GetJson(subId string, host string) (string, string, err
 	}
 
 	// Prepare statistics
+	now := time.Now().UnixMilli()
 	for index, clientTraffic := range clientTraffics {
 		if index == 0 {
 			traffic.Up = clientTraffic.Up
 			traffic.Down = clientTraffic.Down
 			traffic.Total = clientTraffic.Total
-			traffic.ExpiryTime = subscriptionExpiryFromClient(clientTraffic.ExpiryTime)
+			traffic.ExpiryTime = subscriptionExpiryFromClient(now, clientTraffic.ExpiryTime)
 		} else {
 			traffic.Up += clientTraffic.Up
 			traffic.Down += clientTraffic.Down
@@ -139,7 +141,7 @@ func (s *SubJsonService) GetJson(subId string, host string) (string, string, err
 			} else {
 				traffic.Total += clientTraffic.Total
 			}
-			normalized := subscriptionExpiryFromClient(clientTraffic.ExpiryTime)
+			normalized := subscriptionExpiryFromClient(now, clientTraffic.ExpiryTime)
 			if normalized != traffic.ExpiryTime {
 				traffic.ExpiryTime = 0
 			}
diff --git a/sub/subService.go b/sub/subService.go
index 706ef3b8..306d724f 100644
--- a/sub/subService.go
+++ b/sub/subService.go
@@ -108,13 +108,13 @@ func (s *SubService) GetSubs(subId string, host string) ([]string, int64, xray.C
 		}
 	}
 
-	// Prepare statistics
+	now := time.Now().UnixMilli()
 	for index, clientTraffic := range clientTraffics {
 		if index == 0 {
 			traffic.Up = clientTraffic.Up
 			traffic.Down = clientTraffic.Down
 			traffic.Total = clientTraffic.Total
-			traffic.ExpiryTime = subscriptionExpiryFromClient(clientTraffic.ExpiryTime)
+			traffic.ExpiryTime = subscriptionExpiryFromClient(now, clientTraffic.ExpiryTime)
 		} else {
 			traffic.Up += clientTraffic.Up
 			traffic.Down += clientTraffic.Down
@@ -123,7 +123,7 @@ func (s *SubService) GetSubs(subId string, host string) ([]string, int64, xray.C
 			} else {
 				traffic.Total += clientTraffic.Total
 			}
-			normalized := subscriptionExpiryFromClient(clientTraffic.ExpiryTime)
+			normalized := subscriptionExpiryFromClient(now, clientTraffic.ExpiryTime)
 			if normalized != traffic.ExpiryTime {
 				traffic.ExpiryTime = 0
 			}
@@ -133,12 +133,12 @@ func (s *SubService) GetSubs(subId string, host string) ([]string, int64, xray.C
 	return result, lastOnline, traffic, nil
 }
 
-func subscriptionExpiryFromClient(expiryTime int64) int64 {
+func subscriptionExpiryFromClient(nowMs, expiryTime int64) int64 {
 	if expiryTime > 0 {
 		return expiryTime
 	}
 	if expiryTime < 0 {
-		return time.Now().UnixMilli() + (-expiryTime)
+		return nowMs + (-expiryTime)
 	}
 	return 0
 }
diff --git a/sub/subService_test.go b/sub/subService_test.go
index 32f013fd..d87a198c 100644
--- a/sub/subService_test.go
+++ b/sub/subService_test.go
@@ -5,24 +5,24 @@ import (
 	"encoding/json"
 	"strings"
 	"testing"
-	"time"
 
 	"github.com/mhsanaei/3x-ui/v3/database/model"
 )
 
 func TestSubscriptionExpiryFromClient(t *testing.T) {
-	if got := subscriptionExpiryFromClient(0); got != 0 {
+	const now = int64(1_700_000_000_000)
+	const oneDayMs = int64(86_400_000)
+	if got := subscriptionExpiryFromClient(now, 0); got != 0 {
 		t.Fatalf("zero expiry should stay zero, got %d", got)
 	}
-	if got := subscriptionExpiryFromClient(1_700_000_000_000); got != 1_700_000_000_000 {
+	if got := subscriptionExpiryFromClient(now, 1_700_000_000_000); got != 1_700_000_000_000 {
 		t.Fatalf("positive expiry should pass through, got %d", got)
 	}
-	const oneDayMs = int64(86_400_000)
-	before := time.Now().UnixMilli()
-	got := subscriptionExpiryFromClient(-oneDayMs)
-	after := time.Now().UnixMilli()
-	if got < before+oneDayMs || got > after+oneDayMs {
-		t.Fatalf("delayed-start expiry should land ~1 day from now, got %d (window %d..%d)", got, before+oneDayMs, after+oneDayMs)
+	if got := subscriptionExpiryFromClient(now, -oneDayMs); got != now+oneDayMs {
+		t.Fatalf("delayed-start expiry should be now+|value|, got %d, want %d", got, now+oneDayMs)
+	}
+	if a, b := subscriptionExpiryFromClient(now, -oneDayMs), subscriptionExpiryFromClient(now, -oneDayMs); a != b {
+		t.Fatalf("same now+value should be deterministic across calls, got %d vs %d (#4545 review)", a, b)
 	}
 }
 
diff --git a/web/service/client.go b/web/service/client.go
index b25854d6..0bdf6cc2 100644
--- a/web/service/client.go
+++ b/web/service/client.go
@@ -222,9 +222,7 @@ func (s *ClientService) SyncInbound(tx *gorm.DB, inboundId int, clients []model.
 			if incoming.Auth != "" {
 				row.Auth = incoming.Auth
 			}
-			if incoming.Flow != "" {
-				row.Flow = incoming.Flow
-			}
+			row.Flow = incoming.Flow
 			if incoming.Security != "" {
 				row.Security = incoming.Security
 			}
diff --git a/web/service/client_sync_multiprotocol_test.go b/web/service/client_sync_multiprotocol_test.go
index 335c7e82..cb4e1f37 100644
--- a/web/service/client_sync_multiprotocol_test.go
+++ b/web/service/client_sync_multiprotocol_test.go
@@ -31,8 +31,9 @@ func TestSyncInbound_PreservesCredentialsAcrossProtocols(t *testing.T) {
 	const sharedEmail = "shared@example.com"
 	const wantUUID = "ce8d33df-3a64-4f10-8f9b-91c3a8e0c001"
 	const wantAuth = "h2-auth-token"
+	const wantFlow = "xtls-rprx-vision"
 
-	vlessClient := model.Client{Email: sharedEmail, ID: wantUUID, Enable: true, Flow: "xtls-rprx-vision"}
+	vlessClient := model.Client{Email: sharedEmail, ID: wantUUID, Enable: true, Flow: wantFlow}
 	if err := svc.SyncInbound(nil, vlessInbound.Id, []model.Client{vlessClient}); err != nil {
 		t.Fatalf("vless SyncInbound: %v", err)
 	}
@@ -52,7 +53,61 @@ func TestSyncInbound_PreservesCredentialsAcrossProtocols(t *testing.T) {
 	if row.Auth != wantAuth {
 		t.Errorf("Auth not persisted: got %q, want %q", row.Auth, wantAuth)
 	}
-	if row.Flow != "xtls-rprx-vision" {
-		t.Errorf("Flow was clobbered by Hysteria sync: got %q, want xtls-rprx-vision", row.Flow)
+
+	vlessList, err := svc.ListForInbound(nil, vlessInbound.Id)
+	if err != nil {
+		t.Fatalf("ListForInbound(vless): %v", err)
+	}
+	if len(vlessList) != 1 || vlessList[0].Flow != wantFlow {
+		t.Errorf("VLESS inbound should still report flow=%q via FlowOverride, got %#v", wantFlow, vlessList)
+	}
+
+	hysteriaList, err := svc.ListForInbound(nil, hysteriaInbound.Id)
+	if err != nil {
+		t.Fatalf("ListForInbound(hysteria): %v", err)
+	}
+	if len(hysteriaList) != 1 || hysteriaList[0].Flow != "" {
+		t.Errorf("Hysteria inbound should report empty flow, got %#v", hysteriaList)
+	}
+}
+
+func TestSyncInbound_AllowsClearingFlow(t *testing.T) {
+	dbDir := t.TempDir()
+	t.Setenv("XUI_DB_FOLDER", dbDir)
+	if err := database.InitDB(filepath.Join(dbDir, "3x-ui.db")); err != nil {
+		t.Fatalf("InitDB: %v", err)
+	}
+	t.Cleanup(func() { _ = database.CloseDB() })
+
+	db := database.GetDB()
+
+	vless := &model.Inbound{Tag: "vless-in", Enable: true, Port: 10003, Protocol: model.VLESS}
+	if err := db.Create(vless).Error; err != nil {
+		t.Fatalf("create vless inbound: %v", err)
+	}
+
+	svc := ClientService{}
+	const email = "alice@example.com"
+	const uid = "ce8d33df-3a64-4f10-8f9b-91c3a8e0c002"
+
+	withFlow := model.Client{Email: email, ID: uid, Enable: true, Flow: "xtls-rprx-vision"}
+	if err := svc.SyncInbound(nil, vless.Id, []model.Client{withFlow}); err != nil {
+		t.Fatalf("vless SyncInbound (set flow): %v", err)
+	}
+
+	cleared := model.Client{Email: email, ID: uid, Enable: true, Flow: ""}
+	if err := svc.SyncInbound(nil, vless.Id, []model.Client{cleared}); err != nil {
+		t.Fatalf("vless SyncInbound (clear flow): %v", err)
+	}
+
+	list, err := svc.ListForInbound(nil, vless.Id)
+	if err != nil {
+		t.Fatalf("ListForInbound: %v", err)
+	}
+	if len(list) != 1 {
+		t.Fatalf("expected 1 client, got %d", len(list))
+	}
+	if list[0].Flow != "" {
+		t.Errorf("flow should be clearable on the owning inbound, got %q (Copilot review on #4545)", list[0].Flow)
 	}
 }