Greetings!
This is Tin, I'll do my best to help. Sometimes it happened, I will suggest you to try to use other browser and check if it will help you to unsubscribe. May I know if you're using Outlook app?
Please try to open that email via browser and try to unsubscribe from there. And if it didn't work, better to reach AllEvents Support regarding this remove your email from their mailing list.
Thanks,
Tin