Every time I create a new folder and relocate, then relink media, it works again.
By the end of this edit I’m going to have to go:
My Computer > Project > Prores > Prores > Prores > Prores > Prores > Prores > Prores > Prores > Prores > Prores > Prores > Prores > Prores > Prores > Prores > Prores > Prores
…to find the media!