I've added more debug, looks like everything pinpoints an issue in readDataPacket.

Either the check byte or stop mark are wrong/weird, maybe some timing issue but I doubt. adding a startSession after the first sendCommand fix the second one, but doing so for the others leads to a segfault, so there is definitely something going on with the buffers.

The repository is up to date, the two serial logs has been uploaded here.

I'm giving up (for now maybe...) I can't understand what's going on, and I'm wasting too much time on that.