HA begun restarting for minutes - websocket connection failed

since weeks ago, my HA begun restarting for minutes. Developer tools / console in the browser under F12 shows the following, about 40 instances, after that it drops the attempt and HA starts in three seconds. I am running on Synology VMM. Any ideas where to go? It might be linked to lovelace as the core.2895f1d4.js seems to be related to lovelace.

I tried to disable all integrations and add-ons to turn them on step by step and check what causes the problem. No change. The delay is happening even when everything is disabled and turned off. So this seems to me to be related to some “HA core”

Funny, fresh install without anything returns two failed attempts but then restarts quickly.