Can you share the file? Sketch imports can have some structural issues which would cause this error. You can talk to Figma support team about it via support request form.
Huh, well thanks for checking, its working fine for me too now - pretty sure I haven’t touched the project since posting this topic… Anyway I appreciate the time taken to have a look.
For the record I originally was using the desktop app and then tested again in Safari. Both had the same issue.