OK, I went back to the project that was causing the aforementioned problem.

Still a problem. But I noticed there were copied MIDI tracks using the same channel which on my PERFORMING machine would have been routed to different ports on my hardware MIDI output device.

However, this was my recording machine, where I typically develop MIDI using a soft synth (no hardware MIDI outputs at all)

I deleted the MIDI tracks and the problem went away!

If I had realized that was going to happen I might have experimented a bit to learn exactly what had to change in order to fix the problem. (I'm thinking deleting all the MIDI was wayyyy overkill, but...)

Afterwards, I recreated the MIDI tracks without recreating the problem... except this time none of them sent data to the same channel.

I'm wondering if somewhere in memory there was still a reference to multiple ports, even though it didn't show up in any of the dialog boxes... and since there weren't multiple ports available on this machine, it caused a logic error for which there was no error checking...?

anyway, this may provide a starting point for anyone else who experiences similar stuttering and lockup symptoms.

The project, by the way, was a cover of the Elvin Bishop song "Fooled around and fell in love", and I'm pretty happy with the way it turned out... it's all real band except for some extensive piano-roll entered MIDI to get the signature passages, and my own guitar playing. If we ever get bitCONCERT.com off the ground, it will be one of the first songs I play there.

https://www.dropbox.com/sh/ey71h8ep047758h/AAC12jNM0Hz9Q8zsh5iDeqNHa?dl=0