Onlyoffice Unknown error

Running Nextcloud Apache 19.0.3 under Docker with Traefik 2 as the reverse proxy.

I’m getting the following error trying to get OnlyOffice to open documents:

Unknown error press "OK" to return to Document list.

The weird thing about it is that if I test the OnlyOffice installation from Settings -->ONLYOFFICE I get the following success message:

Settings have been successfully updated (version 5.6)

I’m not really sure where to go from here since I’m not seeing any errors in Nextcloud Logging or any of the OnlyOffice Containers. This used to work when I was running behind a NGINX reverse proxy so I’m not sure this is related to Traefik or not.