I experienced an odd failure mode on my brand-new Thumby after getting it yesterday. While playing a game that uses the greyscale display library (MineSweep from the arcade), a black bar appeared and began rolling vertically up the screen (like if you film a CRT). The bar was maybe four pixels tall and swept up the screen a couple times per second, though the speed changed over time as I interacted with the game. I assumed this was just a timing bug in the greyscale library's display control logic, so I didn't think much of it.

Then, after turning the device off and back on, it entered what appeared to be a boot loop -- the TinyCircuits splash screen appeared for a second, then the display went black for a second, then the splash screen appeared again, etc. But after leaving the device turned off for a few minutes, it turned on properly, and has worked so far since, including in MineSweep.

One final note: before this occurred, I had set the device right next to a cold window (20 F outside). No idea if this could affect operation.

If this happens again I'll record video.

Well, my bad. It occurred to me to check if the battery was low, so I loaded the Battery application from the arcade, and according to it the battery was almost empty. If anything like this happens while the battery is reported as more full, I'll reply again.

That said: it would be a nice feature if the firmware performed a voltage check like that application does and displayed a low-battery icon in the early stages of boot, so the boot-loop that occurs at low battery would be less mysterious.

Well, my bad. It occurred to me to check if the battery was low, so I loaded the Battery application from the arcade, and according to it the battery was almost empty. If anything like this happens while the battery is reported as more full, I'll reply again.

That said: it would be a nice feature if the firmware performed a voltage check like that application does and displayed a low-battery icon in the early stages of boot, so the boot-loop that occurs at low battery would be less mysterious.

I still don't quite understand how to solve your problem.