I was having this issue now for quite a while. and could not figure out why that message spammed so often in the logs.
and it seems it got worse everytime I tried to debug it.. with several logs entries per second.
restarting the web gui (nginx), the docker daemon, the whole array or even a reboot did not fix this.
turns out that I had open the web gui several times, in different browser, locally, on the phone etc. once some kind of error state happens (in my case a full syslog partition), any open websocket (used to show e.g. current cpu load, docker state etc.) would close. and any request to reopen them would trigger such a message (as it misses some context data in the request as described in the article). the problem is, that this reconnect seems to happen constantly, even if you just have the page open somewhere in the browser.
once I closed all browser session the logs stopped. opening the page again seems to properly initialize it and the GUI is finally working.
hope this helps someone.