It's baaa-aaack -- in 9.0.1! Very dismaying. I'm referring to the mysterious bug where MIDI regions won't play back until you reopen the session and see that they've been muted. It happens when you have Create Take Folders activated. I haven't used Create Take Folders in quite a while, and maybe that's why I haven't seen it until now.
So, it's the same as before:
What happens is that certain MIDI regions just stop playing back. They do not appear to be muted (i.e, not grayed-out). Toggling the regions with the Mute Tool does not make them play. Closing the project and reopening same reveals that these particular regions that wouldn't play back are now muted (grayed-out). If you then un-mute them with the tool, they'll playback. No individual notes are muted and I did not choose the pref for software instrument channel strips to be muted independently.
I can also report the same sub-problem as JD where he says:
"I'm using "create take folders." When I record into a region, sometimes all the regions on that track will not play back. The main (top) folder is green, but when I pull the arrow down to see all the takes, all are greyed out. Highlighting them and hitting the "m" key will not change this.
If I quit Logic and restart, then the regions that would not play before do appear as "muted" with the green halo around them and can be made to play again by hitting the "m" key."
Logic Pro X 10.0.4, OSX 10.9, 2012 Retina MacBook Pro, 2.7 GHz i7, 16 GB RAM, 768 GB flash storage, Seagate Thunderbolt drives (sample libraries), Apogee Duet 2, 256K Buffer.