eb_liveDrums: It is possible that small timing differences cause the MIDI Beat Clock to drift. It depends on your computer and is something we can try to improve in future jammr releases. I have added it to the todo list!
If MIDI Beat Clock isn't working for you I suggest disabling it and manually entering the jammr tempo (BPM) value into Ableton so they both use the same tempo. This will ensure you can play in sync although it's less convenient than the MIDI Beat Clock.