Note: This is not a high priority bug report. Restarting the program, as I did while making this post, seemed to fix the issue perfectly. I'm not going to remove the post, however, in case someone in the future runs into a version of this problem that's harder to get rid of.
As a result of the bug I mentioned in my other post (MIDI not working in 2017 version) I reluctantly began using 2019 version again, only to find out that it had a new GUI and the issues I had previously with it (peak meters displaying constant silence despite the presence of sound, for example) were resolved. I'm pretty sure I've been updated to the 2020 version? I'm not sure how that works, and will be making a third post about that.
I was incredibly satisfied and getting used to the program working, but I've discovered a potentially disastrous bug. When I load in one of my MMM projects from back when I was using the 2017 version, the samples (audio objects) seem to discard their timestretch information and play at their original speed. As you might be able to extrapolate, this absolutely wrecks any projects involving samples.
This is likely an error introduced by some change in how the new program handles MMM files. No destructive editing happens to the audio objects, and when I load the MMM file back up in the 2017 version, the samples play fine.
The pitchshift information seems to be preserved perfectly fine.