diff --git a/internal/api/summarydashboard.go b/internal/api/summarydashboard.go
index 3dfcbe7d..4cb48278 100644
--- a/internal/api/summarydashboard.go
+++ b/internal/api/summarydashboard.go
@@ -282,10 +282,12 @@ func (a *summaryAcc) finalize(id string, now time.Time, allowedStaleness time.Du
 		}
 
 		// A day is overdue when, at its close (clamped to now for today), the newest
-		// OK backup is older than the allowed staleness. Days before the first OK
-		// backup ever are exempt: the scheduler anchors to the first real run. A day
-		// where a late backup finally lands renders as backed-up, so checking only the
-		// day's close loses nothing visible.
+		// OK backup is older than the allowed staleness AND the day had no OK backup
+		// of its own. Days before the first OK backup ever are exempt: the scheduler
+		// anchors to the first real run. Requiring the day itself to be empty keeps
+		// sub-daily schedules honest: an hourly plan whose last run was at noon still
+		// backed the day up even though midnight is well past the allowed gap, so the
+		// day must render as backed-up, not overdue.
 		if allowedStaleness > 0 {
 			checkpoint := day.AddDate(0, 0, 1)
 			if checkpoint.After(now) {
@@ -295,7 +297,11 @@ func (a *summaryAcc) finalize(id string, now time.Time, allowedStaleness time.Du
 				lastOkBackup = okBackupDates[nextOkBackup]
 				nextOkBackup++
 			}
-			bucket.Overdue = !lastOkBackup.IsZero() && checkpoint.Sub(lastOkBackup) > allowedStaleness
+			// lastOkBackup <= checkpoint <= day+1, so lastOkBackup.Before(day) is
+			// exactly "the newest OK backup landed on an earlier day" — this day had none.
+			bucket.Overdue = !lastOkBackup.IsZero() &&
+				lastOkBackup.Before(day) &&
+				checkpoint.Sub(lastOkBackup) > allowedStaleness
 		}
 
 		history = append(history, bucket)
diff --git a/internal/api/summarydashboard_test.go b/internal/api/summarydashboard_test.go
index 39802b13..36edc89a 100644
--- a/internal/api/summarydashboard_test.go
+++ b/internal/api/summarydashboard_test.go
@@ -69,6 +69,22 @@ func TestSummaryOverdueFlags(t *testing.T) {
 			// day closes more than 48h past it.
 			expected: []int{0, 1, 2, 3, 4, 5, 6, 7, 8, 9},
 		},
+		{
+			name:          "sub-daily schedule with a backup each day is never overdue",
+			okBackupDates: []time.Time{at(0, 2), at(1, 2), at(2, 2), at(3, 2), at(4, 2), at(5, 2), at(6, 2), at(7, 2), at(8, 2), at(9, 2)},
+			allowedGap:    75 * time.Minute, // hourly cadence * 1.25 grace
+			// Every day has an OK backup at 02:00. Its close (midnight) is ~22h past
+			// that, far beyond the gap, but a day that backed up is never overdue.
+			expected: nil,
+		},
+		{
+			name:          "sub-daily schedule flags a fully missed day",
+			okBackupDates: []time.Time{at(0, 2), at(1, 2), at(3, 2), at(4, 2), at(5, 2), at(6, 2), at(7, 2), at(8, 2), at(9, 2)}, // day2 missing
+			allowedGap:    75 * time.Minute,
+			// Day 2 has no OK backup of its own and closes far past the allowed gap;
+			// day 3 recovers with its own backup and stays backed-up.
+			expected: []int{2},
+		},
 		{
 			name:          "gap exactly at allowed staleness is not overdue",
 			okBackupDates: []time.Time{at(0, 0), at(2, 0), at(4, 0), at(6, 0), at(8, 0)},
diff --git a/webui/src/features/operations/OperationRow.tsx b/webui/src/features/operations/OperationRow.tsx
index 37bd3128..a0b8d7ce 100644
--- a/webui/src/features/operations/OperationRow.tsx
+++ b/webui/src/features/operations/OperationRow.tsx
@@ -32,6 +32,7 @@ import { toaster } from "../../components/ui/toaster";
 
 import {
   BackupProgressEntry,
+  BackupProgressEntrySchema,
   ResticSnapshot,
   SnapshotSummary,
 } from "../../../gen/ts/v1/restic_pb";
@@ -58,7 +59,7 @@ import {
 import { OperationIcon } from "./OperationIcon";
 import { LogView } from "../../components/common/LogView";
 
-import { create } from "@bufbuild/protobuf";
+import { create, toJsonString } from "@bufbuild/protobuf";
 import { useReposByGuid } from "../../app/provider";
 import { OperationListView } from "./OperationListView";
 import * as m from "../../paraglide/messages";
@@ -737,7 +738,14 @@ const BackupOperationStatus = ({
     );
   } else {
     console.error("GOT UNEXPECTED STATUS: ", status);
-    return <>{m.op_row_unexpected_status() + JSON.stringify(status)}</>;
+    // Serialize via the proto helper: BackupProgressEntry carries int64 fields that
+    // become BigInt, which raw JSON.stringify cannot serialize (it throws).
+    return (
+      <>
+        {m.op_row_unexpected_status() +
+          toJsonString(BackupProgressEntrySchema, status)}
+      </>
+    );
   }
 };