New post, to let you know about the update:
I’ve found a workaround for that: Use the EditorUtilityBase class as parent. On both Construction Script and Begin Play, execute a custom event that starts a Timer (Set Timer by Event) with Looping == true and smallest possible Time (like 0.01). Then it works both in editor and in game!
**Update: **Scratch that. It was working only when the actor BP was opened in the tab. 
When drag&dropped into a level, it doesn’t work without keeping the blueprint opened.