Interesting to note, in case anyone else runs into this.
I did some field recordings on a trip for some rare percussion my retired percussionist friend had. I tried to get 10 random samples per "articulation". Sometimes I got less.
For example, I recorded a conch shell, and have short, long, longer samples. For some reason, I only got 6 long samples, but I have 10 shorts. I figured since they are in different groups, I could use all the samples for either one since they are on different keys.
It ends up that once the <groups> element is defined, it seems that the random feature always loads the maximum number, so the longs don't trigger when the random number is higher than 6.
I'm not sure there is an easy fix since I assume the random number generator is global, but maybe there is a solution. For now, I'm just going to repeat the samples in the shorts group.