For any Push 1 users planning to upgrade to Live 9.6, the following bug with which makes Push inoperable.
When selecting "Slice to Drum Rack" from Simpler while in Slice mode, the track is converted to drum rack in Live as expected, however at same time all buttons on Push 1 go blank and become unresponsive, and a message "Live is showing a dialog that needs you attention" is shown on Push display. No dialog appears on Live console, preventing any action.
Power cycling Push does not correct the error. The only way to restore functionality to Push is to save the project and restart Live. This however is only a temporary fix, as the same error occurs as soon as choose "Slice to Drum Rack" from Simpler again.
I have raised a ticket with Ableton support, and they have confirmed that this is a bug and have escalated to development team for resolution.
If you use the Simpler "Slice to Drum Rack" feature, and have Push 1, I would recommend not upgrading to Live 9.6 until Ableton release a fix.
(Note: as I only have Push 1, I do not know whether this is also a bug on Push 2).