Noticed a certain percentage of cases when the reminder doesn't trigger

We have FormAction with 7 fields. Requesting last slot creates remainder:

date = + datetime.timedelta(seconds=15)
                return default_slots + [ReminderScheduled(

For most cases it works properly, but for some cases it doesn’t trigger and there weren’t any errors in logs. Could you tell how to catch this type of errors? Do I have to check Rabbit messages?