Exactly ... and this is the step that you have to intervene:   if the connection-handle is bad, it basically means that the connection has dropped on one side or the other.   The plugin will attempt to re-establish the connection and you must see to it that it does so correctly.   If the credentials are still known-good, it’s not actually “for authentication reasons,” even though it may present itself that way.   A check of both the database and the web-server logs would be a good place to start sleuthing.   Even if for whatever reason (SQL server down, etc.) the connection truly can’t be re-established now, your Dancer app still must manage to do the right thing, or at least a graceful thing.

This is a common issue with long-running persistent processing of any sort, and the symptoms presented definitely can be red-herrings.   Since you know that the credentials you have available to you are good, then you know that the message ... isn’.t.   If you chase the wrong presumption, you’re chasing a rabbit.   (Been there, etc.)