In case others are also tearing their hair out, todays performance issues look to be confined the EU data hosting, and US seems to be fine.
Please could others post on here if they have other data hosting regions, and whether the data is behaving as expected. It might help to narrow down where the issue lies.
@DanielFox1 look to be some more niggles in the system today. anyone else getting feature service errors?
We seem to be having problems with our EU hosted AGOL instance again this morning. It would be interesting to know if others are experiencing issues again too. The problems are very similar to the issues encountered last Friday (everything is very slow, layers won't display in Web Maps, hosted feature layers say that they are broken or unavailable, scheduled Notebooks are failing to run).
I've logged a support case with EsriUK but haven't heard anything yet.
We're also having the same issue with some of our hosted layers.