Level Sequence spending long time validating assets

Hi

After migrating our animation project from 5.7 -> 5.8 we notice that some level seqeunces take much longer to save (during validation stage). This issue only exhibits when using control rigs in animation mode. Some users have reported it taking up to 30 minutes on some shots, though I have only reproduced it taking 2-3 minutes. These save level sequences in 5.7 would have taken only serveral seconds to save. I attach a simplified repro project which takes about 10 seconds. The more characters the (exponentially) longer it takes to save.

1. Open attached project
2. Open level sequence `/xxxxxxxxx`
3. Enter animation mode
4. Press Save Level Sequence
5. Observe that it takes about 10-15 seconds to save
6. Return to selection mode
7. Press save again
8. Observe that it saves much quicker