I just updated to Ableton 11, only to find 10 keys did not function, and one key crashed any VST loaded. After wasting much time, I shut Live down and put a midi logger on, and found all the keys were sending perfectly good note on/off messages.
I reloaded V10 (having optimistically removed it) and everything worked as it should do. Clearly V11 and the Keylab have some change to their interaction, but as yet it's not obvious what it is. However, short of working with 4 note scales, I am switching back to V10.
I can't see anything in release notes at this stage to explain this, but for other users of the combination it would seem that Live 11 is not a 'drop in ' update.