At one time this happened with my MiniBrute.
While trying to figure out if the Gate Source switch (at the back) was in the wrong position (like in the Audio, though I had nothing plugged into the Audio input), I ended up finding that the issue was actually related with that switch and its ambiguous position, so although it looked like it was in the KBD position, internally it seemed like there was still a bit of contact causing the HOLD position to sometimes activate.
After juggling the switch a bit to each side, the issue went away.
So, I'm not sure if this is related with your issue but just in case, that's a simple thing to do or to check.