Is there a way for a DM to see changes made to a player’s character sheet? I suspect some foul play and would like to investigate. If not, I believe this would be a nice tool. Not sure if this is something that is stored in the background and would be simple to pull off. 
This could alternatively be used to monitor for errors on a character sheet, not just for tracking nefarious deeds. 

There is no such log, and as far as I'm aware no such data is stored about character sheets.