Hi,
I had a drver who was stuck at 96% of training.
My training time was set at very high which is the equivalent of 5% per race.
Even after a season he was still stuck at 96%, I had the time to remove plenty of drivers from the academy but his training never improved.
The only to make it reach 100% was to lower the training time at high which is equal to 5% per race.
It's a minor but and the fix given for it is quite simple, you have to adjust the training time in order to get to 100%, the game won't let you achieve more :-)
So if you are at 98%, set your training time to low, and so on....
I hope this helps anyone who faces the same issue.