diff --git a/x-pack/test/alerting_api_integration/common/fixtures/plugins/alerts/server/routes.ts b/x-pack/test/alerting_api_integration/common/fixtures/plugins/alerts/server/routes.ts
index d9e362a99e648..1b92b11eacdcc 100644
--- a/x-pack/test/alerting_api_integration/common/fixtures/plugins/alerts/server/routes.ts
+++ b/x-pack/test/alerting_api_integration/common/fixtures/plugins/alerts/server/routes.ts
@@ -15,7 +15,10 @@ import {
 import { schema } from '@kbn/config-schema';
 import { InvalidatePendingApiKey } from '../../../../../../../plugins/alerts/server/types';
 import { RawAlert } from '../../../../../../../plugins/alerts/server/types';
-import { TaskInstance } from '../../../../../../../plugins/task_manager/server';
+import {
+  ConcreteTaskInstance,
+  TaskInstance,
+} from '../../../../../../../plugins/task_manager/server';
 import { FixtureStartDeps } from './plugin';
 
 export function defineRoutes(core: CoreSetup<FixtureStartDeps>) {
@@ -188,6 +191,40 @@ export function defineRoutes(core: CoreSetup<FixtureStartDeps>) {
     }
   );
 
+  router.put(
+    {
+      path: '/api/alerts_fixture/{id}/reset_task_status',
+      validate: {
+        params: schema.object({
+          id: schema.string(),
+        }),
+        body: schema.object({
+          status: schema.string(),
+        }),
+      },
+    },
+    async (
+      context: RequestHandlerContext,
+      req: KibanaRequest<any, any, any, any>,
+      res: KibanaResponseFactory
+    ): Promise<IKibanaResponse<any>> => {
+      const { id } = req.params;
+      const { status } = req.body;
+
+      const [{ savedObjects }] = await core.getStartServices();
+      const savedObjectsWithTasksAndAlerts = await savedObjects.getScopedClient(req, {
+        includedHiddenTypes: ['task', 'alert'],
+      });
+      const alert = await savedObjectsWithTasksAndAlerts.get<RawAlert>('alert', id);
+      const result = await savedObjectsWithTasksAndAlerts.update<ConcreteTaskInstance>(
+        'task',
+        alert.attributes.scheduledTaskId!,
+        { status }
+      );
+      return res.ok({ body: result });
+    }
+  );
+
   router.get(
     {
       path: '/api/alerts_fixture/api_keys_pending_invalidation',
diff --git a/x-pack/test/alerting_api_integration/security_and_spaces/tests/alerting/index.ts b/x-pack/test/alerting_api_integration/security_and_spaces/tests/alerting/index.ts
index c1f65fab3669e..e8cc8ea699e17 100644
--- a/x-pack/test/alerting_api_integration/security_and_spaces/tests/alerting/index.ts
+++ b/x-pack/test/alerting_api_integration/security_and_spaces/tests/alerting/index.ts
@@ -11,8 +11,7 @@ import { setupSpacesAndUsers, tearDown } from '..';
 // eslint-disable-next-line import/no-default-export
 export default function alertingTests({ loadTestFile, getService }: FtrProviderContext) {
   describe('Alerts', () => {
-    // FLAKY: https://github.com/elastic/kibana/issues/86952
-    describe.skip('legacy alerts', () => {
+    describe('legacy alerts', () => {
       before(async () => {
         await setupSpacesAndUsers(getService);
       });
diff --git a/x-pack/test/alerting_api_integration/security_and_spaces/tests/alerting/rbac_legacy.ts b/x-pack/test/alerting_api_integration/security_and_spaces/tests/alerting/rbac_legacy.ts
index ef5914965ddce..3db3565374740 100644
--- a/x-pack/test/alerting_api_integration/security_and_spaces/tests/alerting/rbac_legacy.ts
+++ b/x-pack/test/alerting_api_integration/security_and_spaces/tests/alerting/rbac_legacy.ts
@@ -77,6 +77,7 @@ export default function alertTests({ getService }: FtrProviderContext) {
             case 'space_1_all at space1':
             case 'superuser at space1':
             case 'space_1_all_with_restricted_fixture at space1':
+              await resetTaskStatus(migratedAlertId);
               await ensureLegacyAlertHasBeenMigrated(migratedAlertId);
 
               await updateMigratedAlertToUseApiKeyOfCurrentUser(migratedAlertId);
@@ -92,6 +93,7 @@ export default function alertTests({ getService }: FtrProviderContext) {
               await ensureAlertIsRunning();
               break;
             case 'global_read at space1':
+              await resetTaskStatus(migratedAlertId);
               await ensureLegacyAlertHasBeenMigrated(migratedAlertId);
 
               await updateMigratedAlertToUseApiKeyOfCurrentUser(migratedAlertId);
@@ -115,6 +117,7 @@ export default function alertTests({ getService }: FtrProviderContext) {
               });
               break;
             case 'space_1_all_alerts_none_actions at space1':
+              await resetTaskStatus(migratedAlertId);
               await ensureLegacyAlertHasBeenMigrated(migratedAlertId);
 
               await updateMigratedAlertToUseApiKeyOfCurrentUser(migratedAlertId);
@@ -140,6 +143,21 @@ export default function alertTests({ getService }: FtrProviderContext) {
               throw new Error(`Scenario untested: ${JSON.stringify(scenario)}`);
           }
 
+          async function resetTaskStatus(alertId: string) {
+            // occasionally when the task manager starts running while the alert saved objects
+            // are mid-migration, the task will fail and set its status to "failed". this prevents
+            // the alert from running ever again and downstream tasks that depend on successful alert
+            // execution will fail. this ensures the task status is set to "idle" so the
+            // task manager will continue claiming and executing it.
+            await supertest
+              .put(`${getUrlPrefix(space.id)}/api/alerts_fixture/${alertId}/reset_task_status`)
+              .set('kbn-xsrf', 'foo')
+              .send({
+                status: 'idle',
+              })
+              .expect(200);
+          }
+
           async function ensureLegacyAlertHasBeenMigrated(alertId: string) {
             const getResponse = await supertestWithoutAuth
               .get(`${getUrlPrefix(space.id)}/api/alerts/alert/${alertId}`)