diff --git a/frontend/src/pages/xray/BalancerFormModal.vue b/frontend/src/pages/xray/BalancerFormModal.vue
index a0b8b032..6e798f07 100644
--- a/frontend/src/pages/xray/BalancerFormModal.vue
+++ b/frontend/src/pages/xray/BalancerFormModal.vue
@@ -61,16 +61,6 @@ const isValid = computed(
   () => !tagEmpty.value && !duplicateTag.value && !emptySelector.value,
 );
 
-const fallbackSupported = computed(
-  () => form.strategy === 'leastPing' || form.strategy === 'leastLoad',
-);
-
-watch(() => form.strategy, (next) => {
-  if (next !== 'leastPing' && next !== 'leastLoad') {
-    form.fallbackTag = '';
-  }
-});
-
 const tagValidateStatus = computed(() => {
   if (tagEmpty.value) return 'error';
   if (duplicateTag.value) return 'warning';
@@ -121,8 +111,8 @@ const okText = computed(() =>
         </a-select>
       </a-form-item>
 
-      <a-form-item label="Fallback" :help="fallbackSupported ? '' : 'Available only with Least ping / Least load'">
-        <a-select v-model:value="form.fallbackTag" allow-clear :disabled="!fallbackSupported">
+      <a-form-item label="Fallback">
+        <a-select v-model:value="form.fallbackTag" allow-clear>
           <a-select-option v-for="tag in ['', ...outboundTags]" :key="tag || '__empty'" :value="tag">
             {{ tag || `(${t('none')})` }}
           </a-select-option>
diff --git a/frontend/src/pages/xray/BalancersTab.vue b/frontend/src/pages/xray/BalancersTab.vue
index 255ed108..1f4fe620 100644
--- a/frontend/src/pages/xray/BalancersTab.vue
+++ b/frontend/src/pages/xray/BalancersTab.vue
@@ -133,23 +133,25 @@ function syncObservatories() {
     delete t.observatory;
   }
 
-  const leastLoads = balancers.filter((b) => b.strategy?.type === 'leastLoad');
-  if (leastLoads.length > 0) {
+  const burstFeeders = balancers.filter((b) => {
+    const type = b.strategy?.type || 'random';
+    return type === 'leastLoad' || type === 'random' || type === 'roundRobin';
+  });
+  if (burstFeeders.length > 0) {
     if (!t.burstObservatory) {
       t.burstObservatory = JSON.parse(JSON.stringify(DEFAULT_BURST_OBSERVATORY));
     }
-    t.burstObservatory.subjectSelector = collectSelectors(leastLoads);
+    t.burstObservatory.subjectSelector = collectSelectors(burstFeeders);
   } else {
     delete t.burstObservatory;
   }
 }
 
 function buildWireBalancer(form) {
-  const supportsFallback = form.strategy === 'leastPing' || form.strategy === 'leastLoad';
   const out = {
     tag: form.tag,
     selector: [...form.selector],
-    fallbackTag: supportsFallback ? form.fallbackTag : '',
+    fallbackTag: form.fallbackTag || '',
   };
   if (form.strategy && form.strategy !== 'random') {
     out.strategy = { type: form.strategy };
@@ -218,11 +220,11 @@ const showObsEditor = computed(() => hasObservatory.value || hasBurstObservatory
 
 const obsView = ref('observatory');
 
-// Keep the radio selection valid as observatories appear/disappear —
-// e.g. deleting the last leastPing balancer should flip the editor to
-// the burstObservatory pane instead of leaving it pointing at the
-// (now-removed) observatory key.
-watch(showObsEditor, () => {
+// Watch each flag individually — watching showObsEditor (OR of the two)
+// misses the case where one observatory swaps for the other in the same
+// tick, leaving obsView pointing at a now-deleted key and JsonEditor
+// trying to parse an empty string.
+watch([hasObservatory, hasBurstObservatory], () => {
   if (obsView.value === 'observatory' && !hasObservatory.value && hasBurstObservatory.value) {
     obsView.value = 'burstObservatory';
   } else if (obsView.value === 'burstObservatory' && !hasBurstObservatory.value && hasObservatory.value) {