Ok time to chime in my tupence.
So this issue affects all pioneer drivers in 64bit from what I can discern reading around. It was the same with the original 900NXS too that I had.
That said, I think it should be noted that it does not breakdown MIDI entirely, nor the python scripting Ableton uses for most of its out-of-the-box controllers.
In fact it just breaks the triggering of MIDI notes to a synth or rack from an external controller. I think by not recognising a Note Off command on the 1st triggered note, being caught in a loop and dismissing all further Note On's.
So, with my Push 1, if you use a Drum Rack, the 1st pad you press plays, you even get the step sequencer running where you can edit the sequence without issue for this single pad. You can use the length of loop change pads without a problem... everything else works, but you can't change pad/drum you are triggering, nor play a beat with your fingers.
All the pages work fine for the different modes and knobs. You can trigger previously created clips in Session View, create tracks, effects, etc... everything but change the 1st MIDI note you touch in Note Mode.
What makes me think it's a Note Off issue is if it's a Synth, as mentioned previously by someone the note continues to infinity or until you switch off the device and back on again, or change soundcard in prefs.
This only happens with Pioneer equipment and their ASIO drivers in my experience, but I'm not saying it's a Pioneer problem alone, something is wrong but I sincerely hope someone is working with guys at Ableton too because for industry standard club gear it doesn't make us confident to experiment at home with complicated setups we can't use in the real world.
Thanks for your eyes