Reported in: https://forum.matomo.org/t/make-oops-there-was-a-problem-during-the-request-dismissible/35390 - I've also experienced this a few times.
In version 3.13.0 the error message “Oops… there was a problem during the request. …” always appears on top of the Dashboard after I woke up my laptop. I assume the reason is that the Wifi connection needs more time to reestablish.
It would be great if I could close that message, since everything (including Ajax like Visits in Real-Time) actually works without problem. Alternatively, the message could simply disappear after a few seconds.
I'm not actually sure how to reproduce it consistently but I often get this:
I guess this is related to https://github.com/matomo-org/matomo/issues/15287 . Happens in Firefox but not in chrome.