Capella breaks when ReqIF.ForeignID attribute values contain non-numerical characters, I’ve written a bit about it at Import/Export ReqIF - #16 by huvrhxlerukmgoymuc. This attribute usually contains requirement IDs in the authoring tool, so you’d have to make Polarion export these as numbers-only values or export the requirement IDs into a different attribute. If there’s no such setting, you could do a regex replace on the .reqif file before import.