Can you put a example? a drill, which one are you trying to use, because the XP provided by each drill, depend on 3 factors.
One is the collapse I mentioned, and this comes from the old system, which reduced the XP gaining once a player, gained a main star level. Now, the drill reduces the XP gain, oonce the involved skills, win a star, so a drill affecting 1 skill, would reduce every time you win a 20% for that skill. If the drill involves 2 skills, the reduction is, at every 40%, if 3, at every 60 and so.
The level of your player skills is like, 8*, so, probably thats why this happens.
Then another factor affecting is the age, based on 3 year slabs, 18-20 21-23 etc there's a reduction but he have 20 years... not sure if you really tested if he's a fast trainer....
Try to share a drill capture, so others can help you better too.