Hello! I recently had this issue in the older version of Fleece, but I spent the majority of the day today updating it and making sure no features I had were broken.

After updating Fleece the issue still persisted, here's a screenshot showing the specific error:

Essentially, when I tried to add a jumper to a custom ScriptableObject that I could create and edit in the inspector it will clear itself upon resetting the unity client. It works normally if I run the editor window though.
The error flag pops up whenever I click on one of those windows and it's calling out Jumper.cs, line 180 as  causing the issue, that and UnityEditor.Undo:RecordObjects(Object[], String)

Letting me know that the "UndoObjects may not be null"

Not sure why this is happening and would appreciate some assistance in identifying the source of the bug. The asset is functioning perfectly otherwise, and I have a few alternative solutions to this that I could take, but would really rather have it be in the inspector because then I can do most of my character work there, rather than in the scene.

Thank you for your time

-Edmang