WEIRD! Time code problem on 2018 project- ALL clips must be slipped

This is the strangest thing I have encountered. I recently moved to a PC- Windows 10- and my Premiere is up to date. A project I did on my mac a while ago (premiere 2018) is completely messed up. Every sequence I've made in the project is off, as though all clips have been slipped. In the one case I examined it was 9 seconds 17 frames off. I had a friend open this on her mac with premiere 2018 and it's still messed up. Other details: was shot in 4K, use proxies but proxies show the same problem as original footage. had some multicam clips which I created to sync, but this is happening in those and in regular clips. Sequence and clips are 23.976. Weirdly... the only clips that align are ones that were shot in slo mo.

Some questions:

-is it possible to slip all clips in a sequence at once? I don't want to spend the next year doing it individually...

-is there anyway to I guess change the reference point on the video so it links up to the right point?

-any other thoughts? 

I should add- NO OTHER PROJECT has this problem. I wonder if there was some weird setting in this project that is causing this problem. I just found some discussion of a bug in 2018 that misaligned time codes but I'm not clear on the fix?? HELP.

Thank you for your time.