Error when I send a message in chat [downgraded to Stable from 3.1.0beta4]

[Stephen]

There are no guarantees of compatibility with anything when using subfolder. It’s an advanced installation and very little is tested against it.

You could use a different subdomain for your discourse installation. SSO will work between subdomains.

The top of the subfolder guide contains this text:

@neil

Discourse Official Statement about Subfolder setup

We support subfolder setups for our hosted customers at the enterprise level and up. Due to heavy technical setup complexity we strongly recommend you do not use this setup unless you are very experienced in custom subfolder setups.

It is critical you have a deep understanding of

• NGINX setup in the Discourse Docker container
• Secure original IP forwarding using custom headers in the proxy chain
• Rate limiting in front proxy server

If this all sounds odd and strange to you we strongly recommend you avoid this setup.

You need to move back to tests-passed to be in a remotely supportable state, assuming your database isn’t just broken now. Rolling back a version is wholly unsupported.