To be honest I'm afraid to try anything because I would be worried not to provoke this issue again. And yes, it was unclear to me too.
But there are few options - one is to tap on the hamburger on the Calendar and to uncheck all calendars there. Still, I don't think that's it, but that you should go to the three dots "???", and tap "Manage accounts". There you could stop Gmail from syncing calendar when you go to its settings, but you could also delete all accounts from there for which you have a calendar. In my case that would be Gmail and Outlook. Note that after AU it appears to be possible to remove even your Microsoft account from there, it wasn't possible before. And then you could restart the phone, and bring back those accounts, and do everything as described above. Also, I don't think that this issue is caused by having multiple calendar accounts, but ok who knows...
Oh, and before trying to remove those accounts, especially the Microsoft account, I would make a backup. Just in case.
But I'm going to ask him right away what he exactly did there so we could know.
As about email live tile, you could try to set separate live tiles for each of your email accounts, I have heard before that users have this issue mostly (or only) when they have one live tile for all their accounts.
Sent from mTalk on Windows 10 phone