partly listing this as a known workaround so people can solve this issue if they come across it, partly reporting a bug.

In some versions of BM, if you attempt to customise your UI with the Seer's Sigil or Divination Sigil (shift-right-click with the sigil in hand, drag around the various boxes, hit save), the game will crash.

This is due to BM attempting to save a file to the folder /config/bloodmagic/ on the client-side, and if this folder is not present, rather than creating it, it crashes. The workaround is to create an empty 'bloodmagic' folder in the config folder, then re-attempt saving your layout.

versions affected:
Bloodmagic-1.20.1-3.3.3-45.jar (maybe others)

see also #2050