Keep losing data assets after changing base class

I keep losing data assets in my project.

Data assets are based on custom C++ class (UDataAsset), and usually after I do couple of changes to the class, after editor restart some of the existing assets disappear from content browser and I see “Failed import” message in output log.

LoadErrors:Error: Error /Game/Maps/testroom : Failed import for SpellConfig /Game/Magic/Spells/SelfCastTest.SelfCastTest

This is getting really annoying and it is quite suboptimal. I’d expect data to persist despite class changes.

Is there a way to fix that? Aside from freezing data asset design, I mean.