I don’t think this is an engine problem, it is most likely a Brushify problem. I have lost count of how many times I have had to rebuild my custom material layers in the Brushify landscape layer blue print…even going back to UE5.0.3. I’m still only using UE5.2.1 for now…and this happened to me just recently after updating a Brushify pack.
The problem I see is Brushify over writes the Landscape layer blueprint when any update from Brushify is applied causing any customization to be lost. I always keep a backup of my project so I can reference anything I have done to the landscape layer if this happens anytime…and then its just a matter of redoing the layers again…just as you have done.