We have, unfortunately, found a nasty bug in the Octatrack MKII firmware (OS 1.30) which can cause the machine to freeze.
The freezing is typically caused by playing back complex pattern data, especially if using rec trigs, while you rapidly move the encoders and/or the crossfader. The GUI will stutter and/or freeze, and the machine will become unresponsive. This can also happen sporadically, but the underlying cause is the same.
We managed to systematically reproduce the issue here and determined that it is a software bug. Our development team are going to start working on a solution this week and should have a new firmware version with a fix ready soon.
Many thanks to those of you who submitted support tickets. With your help, we managed to notice it quickly and were able to reproduce it by reading your descriptions of the problem.