Could you post your About info as actual text? (There’s a little “copy” button in that window.) That makes it so much easier to find/search for this info in the future. 
Hmmm… interesting.
So, in my favorite search engine, I typed in:
"Error while handling Client WS Request: Failed to create DocBroker with docKey"
There were 10 hits, and a few were describing similar symptoms:
- A document that wouldn’t open because of an “open session”.
- Can be seen in the “Admin Console”.
- nginx config problems.
This was one of the closest:
- "Failed to create DocBroker with docKey" When Trying to Open Specific ODS · Issue #523 · nextcloud/richdocuments · GitHub
- Collabora Docker + Nextcloud Docker + NGINX Proxy Manager
Hmmm… perhaps one of those can lead you to a solution.