Refused to send form data to .. because it violates the following Content Security Policy directive: "form-action 'self'"

As of few days, I cannot tell exactly what happened, but I’m unable to load Collabora in Nextcloud anymore.

I’ve been using it for sure on Feb 11th, then I’m not sure if I’ve upgraded the app to 5.0.2 or not, but as of today I’m unable to open documents anymore.

I tried manually downgrading to 5.0.1 (despite not seeing anything which seems related in the changelog), but Nextcloud then goes into maintenance mode and requires upgrade, which takes the app back to 5.0.2.

I tried upgrading Collabora, checking the proxy settings, setting the server_name var in the startup command, but it still won’t load.

In the console log I found the error in topic, which seems the most relevant. But others are below: