Not able to make custom chord shapes in alternate tunings

I am on 4.3.2, on a Mac with Monterey 12.6.3.

I’ve written music in a non-standard tuning for Guitar, but when I try to create chord diagrams for this tuning, the tuning doesn’t “stick” in the Edit Chord Diagrams window and I am unable to select the diagram anyway, unless for every chord diagram I want to make I choose another chord diagram and edit it, every time. I have created the tuning as a Dorico tuning and imported it into the project - the tab notation works perfectly.

Does anyone have any insight into this issue? Thanks.