The Internal Exception Java.IO.IOException error usually occurs when you launch Minecraft, or when the game is underway. This error can be caused by a number of different things.

Minecraft Internal Exception errors can be frustrating to get rid of if you do not know what to do.

The Minecraft launcher may show the ‘Internal Exception Java.IO.IOException’ issue if the Minecraft installation is corrupt or outdated. Moreover, the ...

The error 'Io.Netty.Channel.ConnectTimeoutException' typically appears when Minecraft users attempt to connect to a regular or Realm server. This problem ...

Apparently this is “itzg/mc-monitor” from the same developer, which is built into the image to monitor the server status. For some reason it doesn't work properly with the "Prominence" modpack.