Hey @drPhil !
Spoke to some Media Management folks and they confirmed that leftover backups that need to be could is definitely a reason this could happen.
Edit: It was @Josh Perkoff below that I asked, so his answer is naturally a lot better than mine 
Hello @drPhil This may happen for a couple reasons:
- Fragmented data from previous jobs not yet copied (jobs in a partially copied state or marked for recopy)
- A large amount of secondary data files or baseline files need to be read out & rehydrated for these jobs
- If this is a selective copy, a true-up operation may be in progress
