Is the sign that your websocket is not working. If that happens for all clients, you’ll want to fix that.
The Ajax fallback (the result of above two ports) creates much more load on the system, so you want to get that fixed.
HTTP 422 can have various reasons. My guess, in combination with your information on removed Sessions is that there’s a client that didn’t notice that and still tries to be authenticated and send data.
But I can’t tell from here, it’s a shot in the dark.
After fixing the websockets, the performance should get better. You should also see quite some load on the Zammad processes (especially rails / puma).