Hey!
So I had a similar problem recently.
I made changes to a user-defined struct, saved it and then while referencing that struct in an anim blueprint, I got a crash. I also had an interface that was dependent on that struct which could not be saved due to the crash.
It seems like after you changed your user defined struct ‘Widgets’, you forgot to compile and save your WidgetCreator_Interface which references that struct.
The struct probably got serialized to disk, but because of the crash, the interface couldn’t update the changes to disk.
The solution is to restore a backup of both the struct and interface and try to open the project. It will throw an error saying properties are missing from the struct for other dependent objects. You can then modify your struct and update the interface as required and make sure to save!
Cheers 