Thanks, and sorry, yes I mean patches on the Bass Station. I'll select a saved BS patch and it sounds normal for maybe 30 seconds - then it seems that some parameters suddenly change and it sounds awful.
I haven't touched the Control Surface options in Logic and don't have a separate control surface involved. Just a simple midi over USB setup with the Bass Station.
I've just noticed that I can trigger this behaviour by changing any settings in Logic's "Track Inspector" - if I change Program, Midi Channel, Bank, Volume or even Icon it immediately messes up the BS patch.
I'm not sure what a Midi loop is, although changing patches on the BS behaves as normal.
Thanks!