BUG STATUS: FIXED v16.2.8
While a minor bug that you may not encounter unless you use the Bake Appearance button on the Edit Bones Panel of Duik Bassel, I did want to publish this video explaining a work around in case anyone was unfamiliar with how to deal with expressions when they go bad. It will be fixed in the next release of DUIK in a few weeks.
Links & other information
This bug was first reported in this post: Add Bones Panel bug to be fix in next release.