Audio Tracks turn on and off randomly

I have an mpc 1000 with JJ os XL, and I have the following problem: When I start a new sequence in Next Seq (mode: immediately play), often an random number of the audio tracks that are unmuted in the sequence actually play. When I hit the same sequence again, random tracks turn on and some turn off (only of the ones that are "officially" unmuted). When the sequence loops and starts again, again in a random fashion some can be heard while others can't. I have not recorded track mute, and the tracks seem to be unmuted but still sometimes won't play. Am I doing something wrong? Could it be a certain setting that causes this behaviour, or is it a known bug? Thanks for any help!

It was probably a polyphony issue, as I had some more muted stereo tracks in the sequence, and I wasn't aware that muted audio tracks also affect polyphony. When I got rid of some of the audio tracks that were not needed in the sequence, it got better. However, I am still somewhat confused about the maximum number of tracks that can be played simultaneously.

Think I've experienced something similar. I'm using a riser on a track. In the intro section, no issue, but in the meat of the track with more sounds, I lose playback of a bass and a vocal sample (both halfway through the samples). Also slightly later in the phrase the riser then cuts out.
Same as you no track mutes recorded and in fact no tracks muted anywhere at all. The riser sample is in a different program to the vocal and bass samples, the riser has its own mute group, and each program has Play:POLY and Voice overlap:POLY in the params tab.
I changed a multi-layered snare to a single snare and the samples that were cutting out play fully.
It must be polyphony because if I play single samples over the place where the cutting out had stopped, the samples cut again, so I'm obviously right at the polyphony limit somewhere

I'd like to understand why properly though, the JJOS manual is quite hard to search on polyphony...
MPC2500/JJOS free 3.13