Based on a GM reply, it appears they have a system implemented server side that tracks your Active Fishing activity.
When it reaches certain threshold, it will automatically transfer/teleport you to a designated area where someone will be monitoring if you still continue to cast your rods.
The solution to this is very simple, every X cast / catch, use Task Scheduler to do something else (like change char and read book) or change char & process, then after few hours, go back fishing.
In this way, your fishing session gets resets otherwise, it will be a very huge burden to the server to track everyone who actively fishing 24/7.
If RodCast > 300 Then
ChangeChar()
DoSomething()
Else
CastRod
End If