In the encounters collection, there are a few that I cannot delete. Also, something annoying is that to get to “my encounters” I have to first click off onto “my characters” otherwise if I click encounters, it takes me to dice.

edit: Also, trying to add or subtract monsters from an encounter seems to increment them by 10 instead

Do you have any unnamed campaigns or encounters? If so, give them names and then try to delete. 
As for the other issues, are you using a VPN, browser extensions, or ad blockers? If,so, try disabling them and see if that resolves things. 

No unnamed, and just plain vanilla safari on iOS

edit: I just clicked on one and it just sent me to a page that said unnamed encounter, but I couldn’t do anything with it after that

https://www.dndbeyond.com/encounters/5fa91433-7cc8-4981-95f1-68bc09ed1a1e
that’s one of them if it helps. It said the last changes to the encounter was dec 11th 1969

There has been an issue with these oddly date un-delectable encounters. Thanks for posting a link. If I remember correctly, staff are aware of it. 

Cool, thanks