I just completed many hours of testing, and found that it happens to me with all of the permutations noted above, in a somewhat random fashion. The StageScape also crashes (locks-up) on occasion (about once a day), when switching between various modes (e.g. Monitor, Recording, as well as other menu and tab changes); requiring a full unplug to rectify, so it doesn't boot-up with the 134 App error.
There are obviously some bugs in the software/firmware, which need to be addressed by Line 6. I expect that they are working on it, given that there appear to be dozens of people who have these issues. I also noted the noise problems that were not there in prior versions.
I hope a fix is released soon, as it is no longer usable for important sessions.