I had a player drop from 15-17 determination (sorry, it was 4 or 5 weeks ago so I don't remember exactly) to 8 determination. I got a news item saying it was due to off field incidents. Took me 2 years of tutoring to get it back to something similar again...so yeah it can happen, maybe you missed the news item?
To be honest, prior to the one I mentioned above, I'd only really seen it work the other way around where a player gets a spike in determination due to off field incidents. Was gutted when it dropped!