Multiple Websockets failing on v11.X

[RightiousNewb]

Hoping someone can help if they've run into a similar issue.
I have had a working solution in v10.X using linuxserver.io's SWAG container to set up Nginx as a reverse proxy, and everything seems to work fine on v10.X, but when I switched over to v11.X (I've tried 11.307 and 11.299) I can get into the .../setup page without any problems, but launching a game world fails with:

WebSocket connection to 'wss://foundry.rightiousrealm.duckdns.org/socket.io/?session=06e45b0…&EIO=4&transport=websocket' failed: 
value	@	websocket.js:44
value	@	transport.js:45
value	@	socket.js:164
a	@	socket.js:105
value	@	manager.js:108
(anonymous)	@	manager.js:331

And this retries 6 times before failing out with:

Uncaught (in promise) TypeError: Cannot read properties of null (reading 'sessionId')
    at a.<anonymous> (foundry.js:8454:29)
    at L.emit (index.mjs:136:20)
    at a.value (socket.js:498:20)
    at a.value (socket.js:485:18)
    at a.value (socket.js:455:22)
    at L.emit (index.mjs:136:20)
    at manager.js:207:18
(anonymous)	@	foundry.js:8454
L.emit	@	index.mjs:136
value	@	socket.js:498
value	@	socket.js:485
value	@	socket.js:455
L.emit	@	index.mjs:136
(anonymous)	@	manager.js:207
Promise.then (async)		
it	@	websocket-constructor.browser.js:5
value	@	manager.js:206
L.emit	@	index.mjs:136
value	@	index.js:131
value	@	manager.js:193
L.emit	@	index.mjs:136
value	@	socket.js:324
L.emit	@	index.mjs:136
value	@	transport.js:97
value	@	transport.js:89
ws.onmessage	@	websocket.js:69

I can see in the network inspector of my browser that upon loading the /setup page I get what appears to be a working and healthy websocket, but if I understand correctly, it looks like a new websocket connection is being initiated with the same ID when I try to launch a game world and that is what's causing the failure.

I reached out on the LinuxServer.io discord and they had me update all of my .conf files to make sure it wasn't an old config there causing issues, but it did not resolve the issue. I have since also tried getting things to work with a completely new /data fiile for foundry and I am still experiencing the same issues.

If you have any suggestions or need more info about how my setup is currently configured, please let me know!

EDIT: I've also tried to launch a game world both on and off my local network.