Twiistrz that's a pretty serious issue. There could be many causes for this, but let me give you some insight into what's happening.
A normal request is being processed, while doing so one of the first things is retrieving the access token that identifies you to Flarum. While reading that information from the database the connection to it is abruptly ended. Most of these situations happen when sending php code into a separate process, but that's not something Flarum (currently) does and even if it would the Illuminate component is pretty stable to handle such disconnects.
My guess is that the server is actively disconnecting the Flarum app. Perhaps your database is hosted on another server and there's a huge latency. Perhaps the database connection is disrupted due to aggressive timeout configurations. I'd say, if possible, send this issue over to your Hosting provider support desk and let them check if they see any issues.
Hope this helps.
