This seems to be a pretty long standing bug that severely limits a main functionality. If there is a workaround, I'd be happy to use it in the meantime. But can we get a substantive update on this? Thanks so much! I really love this plugin!
This is an issue for me as well. The error comes from GroupField.php on line 257 according to the error message. Any patch that can be applied? My entire site is built on this and therefore non-functioning at the moment.