I just noticed that problem appeared on some trees where i use overlay. All tress is same model with overlay flag, but only some of all have this problem (maybe about 2-3% of all tress). Before everything work good, I do not change anything in game i only upgrade my gpu with new gtx 1060 and install new nvidia driver, and i think then problem appear.

Any idea what can cause this problem and how i can fix this?

May can I have some more information?
The trees have only the overlay flag? what is with the Alpha channel on the Textur , what Format are you use,?

I had times a similar error, I have for such models DDS with 1bit DXT1,Tried and the error was gone

Try it, and give me modest if anything has done

This is the same model with overlay flag and texture with alpha chanel, dds/tga nevermind - same results (except for dds 1bit where i don't have this problem but result is bad). With PNG texture results is good as before, but png eat to much memory and i want use dds or tga. The good tree next to problematic tree is just copy/paste.

This problem is not related only with this tree model, this happening in whole game, and i think the problem is related to engine or graphic driver, but unfortunately at this moment i do not have second pc to test with diferent graphic card and driver.

The most annoying thing, everything works fine in last five years on different pc, and now i need figure out why this happening

Here i found one my old level picture (the first one) where everything work good, and the second one is with overlay problem.

The problem was in engine build-in OVERLAY function, from some strange reason this problem appears randomly on some models in level when i set overlay flag. Now when i write shader for overlay everything works fine again.