Home Assistant websocket not working

[Linwood]

Is there any way to put the old router back and remove opnsense?

If it still fails the same way you learn a lot.  If it doesn't fail, the packet trace idea is perhaps the best place to go.

You mention running IGMP proxy WAN and LAn, you also talk about a reverse proxy.  Is your access to Home Assistant somehow from the internet and not from your local LAN? What happens if the internet is down (say back with the old router) -- did anything break?

I thought the issue was you can't connect to MQTT -- did that start working?

My suggestion is not at odds with Patrick's but is a different dimension -- pick ONE thing that is a failure you think relates to opnsense, one single thing, and describe it fully, and see if you can get more details including packet traces.   The errors shown look like zigbee related (when I search for bellows for example I get a lot of hits about zigbee).  Are all your poblems actually originating with zigbee?   (The UI -- you mean the HA UI not the Zigbee2MQTT UI?)

Finally, a lot of what you are talking about looks like WAN related stuff.  HA is mostly local (with some cloud integrations of course), and everything you've mentioned should be local.  It would be very helpful if in picking something to concentrate on, pick something unrelated to the internet.  Don't access HA from the internet, access it locally (you are, right?  Not with something thru nabu casa or some proxy?

But... pick one thing that fails and figure out what you can.  MQTT (the service, not zigbee2mqtt) is pretty straightforward -- if HA can't talk to HA, do as I suggested and see if you can, see what happens.   But pick one thing.  And for us to help, try to stick with one specific failure, not jump around.  It will help a lot.