Thankful for your help @[deleted] !
Test 1) Disconnect Cubase MIDI out, problem disappears.
Test 2) Connect Cubase MIDI out, delete Hide button, problem appears.
Test 3) After Test 2, delete all objects from template, problem still appears.
I think this is part of the cause:
I use MIDI Fighter Twister - Bome - Cubase
Only one instance of Bome running (same instance as above)
If I switch tracks in Cubase, something with MIDI channel 1 address 0 makes Chameleon hide.
MIDI Fighter Twister uses MIDI channel 1 address 0 for one of its knobs.