diff --git a/frontend/templates/index.html b/frontend/templates/index.html
index 63be7ac..e5c194b 100644
--- a/frontend/templates/index.html
+++ b/frontend/templates/index.html
@@ -156,7 +156,14 @@ async function runAnalysis(vmid, filename, vmName) {
   }
 
   var analysisId = data.analysis_id;
+  if (!analysisId) {
+    setPhase('Analysis failed', 0, false);
+    showError('Backend returned invalid response — may need restart.');
+    return;
+  }
+
   var startTime = Date.now();
+  var pollErrors = 0;
 
   for (;;) {
     await sleep(2000);
@@ -180,6 +187,16 @@ async function runAnalysis(vmid, filename, vmName) {
         showError(sdata.error_details || 'Analysis failed');
         return;
       }
+      if (sdata.error) {
+        pollErrors++;
+        if (pollErrors > 15) {
+          setPhase('Analysis failed', 0, false);
+          showError('Backend unavailable — analysis may need restart.');
+          return;
+        }
+      } else {
+        pollErrors = 0;
+      }
     } catch (_) {}
   }
 }
diff --git a/frontend/templates/scp.html b/frontend/templates/scp.html
index dcf7b9e..75caf9c 100644
--- a/frontend/templates/scp.html
+++ b/frontend/templates/scp.html
@@ -119,9 +119,15 @@ async function startScpPull(e) {
             btn.disabled = false; return;
           }
           var analysisId = adata.analysis_id;
+          if (!analysisId) {
+            setScpPhase('Analysis failed', 0, false);
+            showScpError('Backend returned invalid response — may need restart.');
+            btn.disabled = false; return;
+          }
           var vmid = document.getElementById('scp-vmid').value;
           var vmName = document.getElementById('scp-vm-name').value.trim();
           var astart = Date.now();
+          var pollErrs = 0;
           for (;;) {
             await new Promise(r => setTimeout(r, 2000));
             var sr = await fetch('/session/analyze/status/' + analysisId);
@@ -141,6 +147,16 @@ async function startScpPull(e) {
               showScpError(sdata.error_details || 'Analysis failed');
               btn.disabled = false; return;
             }
+            if (sdata.error) {
+              pollErrs++;
+              if (pollErrs > 15) {
+                setScpPhase('Analysis failed', 0, false);
+                showScpError('Backend unavailable — analysis may need restart.');
+                btn.disabled = false; return;
+              }
+            } else {
+              pollErrs = 0;
+            }
           }
         }
         if (pdata.phase === 'error') {