It seem that all the workouts, activities, and classes have a count ceiling of 99. This is probably because the UI allows for only 2 digits. I have encountered this on both the run the world all races and the ABS 100% E workout since I tend to do these everyday. I will no doubt run into the ceiling on others but since I mix up the rest of my workouts from day to day it will take longer. I expect that the miles count the the races will top off at 999 since there seems to be only enough room for 3 digits there. I won't run into that for a while since I'm only at 394 miles at the moment. I also wonder if the trophy count will eventually reach a ceiling of 99.
Since this game appears to be something that one would use for a couple of years at least until a newer version comes out, these ceiling limitations don't really encourage sticking with the workout program in the long run.
I've been keeping an eye on this issue for a while and I have some more information to relate. I'm glad to report that the trophy count continues after 99 :-)
On the workouts where I have reached 99 on the workout tile/icon I have noticed something very interesting. On the information screen just before the workout starts I started seeing the number 10 instead of 99. Then after a period of time (I'm assuming after 10 more workouts) it changed to 11 and then to 12. So it seems that that part of the UI is showing the first 2 digits of what should be 100 - 109, 110 -119 and 120 -129 respectively. The good news here is that the game is actually keeping a count of the workouts completed after 99 and it's just the UI that's causing the problem. It also seems that this shouldn't be too difficult to fix.