diff --git a/apps/backend/src/poll/poll/poll.service.ts b/apps/backend/src/poll/poll/poll.service.ts
index 410dd7c0..8547055e 100644
--- a/apps/backend/src/poll/poll/poll.service.ts
+++ b/apps/backend/src/poll/poll/poll.service.ts
@@ -235,7 +235,7 @@ export class PollService implements OnModuleInit {
       if (!oldEvent) {
         return false;
       }
-      return oldEvent.start.valueOf() !== event.start.valueOf() || oldEvent.end.valueOf() !== event.end.valueOf();
+      return oldEvent.start.valueOf() !== new Date(event.start).valueOf() || oldEvent.end.valueOf() !== new Date(event.end).valueOf();
     });
     if (updatedEvents.length > 0) {
       for (const event of updatedEvents) {
@@ -398,7 +398,7 @@ export class PollService implements OnModuleInit {
       $or: events.map(e => ({['selection.' + e._id]: {$exists: true}})),
     };
     await this.participantModel.updateMany(filter, {
-      $unset: events.map(e => 'selection.' + e._id),
+      $unset: events.reduce((acc, e) => ({...acc, ['selection.' + e._id]: ''}), {})
     }, {timestamps: false}).exec();
   }