Looks like it's a floating issue that depends on a preset although I'm still not sure which parameter causes such a conflict.
Nicko, I am not sure about your
floating issue hypothese. My MB freezes in this case no matter which preset is loaded. Even the factory presets are affected. What's more, the currently loaded preset does not even need to have a sequencer preset.
In the meantime, I happened to address the problem as a MIDI (loop?) issue. (Thanks to Lunatic Sound from the vital hint.) My MB is hooked in a bunch of older and newer synths over the
emagic AMT8 fossil. I gave it a try and took the MIDI IN plug out of Matrixbrute. Lo and behold: no GATE freeze issue anymore.
As a bonus, some other responding mysteries are gone, too. For instance, I kept experiencing trouble switching over the <Preset | Seq | Mode> trio. The buttons ware in a way badly responding, so I had to press a button at least twice to switch. I was already assuming a hardware failure. Obviously, this issue was related to the MIDI, too.
So I end up without MIDI IN on Matrixbrute. Since I hardly use IDI IN on MB anyway, this is not a loss. Nor is it worth starting some time-consuming MIDI Loop Chasing.
Hope it helps.
P.S.: My MB is also on 2.0. MIDI out from MB works without any hassle.