Cake Crashes MRCC (and blocks restart)

Yes, ARP sends All Notes Off and All Sounds Off across all MIDI Channels when you press Stop Twice on ARP or when it receives 2 consecutive Stop messages. The All Notes Off, All Sounds Off is commonly used for panic stop. Here is an example log (below). I have a Beatstep Pro connected to ARP over USB. (MIDI Thru is enabled, so I can capture the messages from the BS Pro. I press play, then stop twice. You can see that 3 sets of All Notes Off and All Sounds emitted. 2 are from the BS Pro and one is from ARP.

MIDI controllers typically send on all MIDI channels because there is no way of knowing if you've recently changed MIDI channel and there may still notes playing on any channel (Note OFFs pending). There's no timing issue with spamming this many messages, because you've told the music to stop.

TIMESTAMP IN PORT STATUS DATA1 DATA2 CHAN NOTE EVENT

270312 3 -- 250 --- --- -- --- Start

270314 3 -- 148 70 60 5 Bb 4 Note On (ARP)

270315 3 -- 248 --- --- -- --- Timing Clock

270330 3 -- 248 --- --- -- --- Timing Clock

270350 3 -- 248 --- --- -- --- Timing Clock

270369 3 -- 248 --- --- -- --- Timing Clock

270389 3 -- 248 --- --- -- --- Timing Clock

270408 3 -- 248 --- --- -- --- Timing Clock

270428 3 -- 248 --- --- -- --- Timing Clock

270447 3 -- 248 --- --- -- --- Timing Clock

270467 3 -- 248 --- --- -- --- Timing Clock

270486 3 -- 248 --- --- -- --- Timing Clock

270505 3 -- 248 --- --- -- --- Timing Clock

270525 3 -- 248 --- --- -- --- Timing Clock

270545 3 -- 248 --- --- -- --- Timing Clock

270565 3 -- 248 --- --- -- --- Timing Clock

270583 3 -- 248 --- --- -- --- Timing Clock

270603 3 -- 248 --- --- -- --- Timing Clock

270623 3 -- 248 --- --- -- --- Timing Clock

270642 3 -- 248 --- --- -- --- Timing Clock

270655 3 -- 252 --- --- -- --- Stop

270655 3 -- 132 70 60 5 Bb 4 Note Off  (ARP)

270655 3 -- 176 120 0 1 --- CC: All Sound Off

270655 3 -- 176 123 0 1 --- CC: All Notes Off

270656 3 -- 177 120 0 2 --- CC: All Sound Off

270656 3 -- 177 123 0 2 --- CC: All Notes Off

...

270687 3 -- 190 120 0 15 --- CC: All Sound Off

270689 3 -- 190 123 0 15 --- CC: All Notes Off

270689 3 -- 191 120 0 16 --- CC: All Sound Off

270691 3 -- 191 123 0 16 --- CC: All Notes Off

270947 3 -- 252 --- --- -- --- Stop

270949 3 -- 176 120 0 1 --- CC: All Sound Off

270950 3 -- 176 123 0 1 --- CC: All Notes Off

270951 3 -- 177 120 0 2 --- CC: All Sound Off

270951 3 -- 177 123 0 2 --- CC: All Notes Off

...

270976 3 -- 190 120 0 15 --- CC: All Sound Off

270977 3 -- 190 123 0 15 --- CC: All Notes Off

270978 3 -- 191 120 0 16 --- CC: All Sound Off

270979 3 -- 191 123 0 16 --- CC: All Notes Off

270988 3 -- 176 120 0 1 --- CC: All Sound Off      (ARP)

270988 3 -- 176 123 0 1 --- CC: All Notes Off      (ARP)

270989 3 -- 177 120 0 2 --- CC: All Sound Off      (ARP)

270989 3 -- 177 123 0 2 --- CC: All Notes Off      (ARP)

...

271040 3 -- 190 120 0 15 --- CC: All Sound Off      (ARP)

271041 3 -- 190 123 0 15 --- CC: All Notes Off      (ARP)

271042 3 -- 191 120 0 16 --- CC: All Sound Off      (ARP)

271043 3 -- 191 123 0 16 --- CC: All Notes Off      (ARP) I realize this doesn't help the crash problem with MRCC. But I think Submo is right that it explains the CC messages you are seeing. From the MIDI Standard: 120 = All Sound Off (It does so regardless of release time or sustain. (See MIDI CC 123)) 123 = All Notes Off (Release time will still be maintained, and notes held by sustain will not turn off until sustain pedal is depressed.)