Landscape Paint material with a big question mark?

I did a recompileshaders all. It took 2-3 minutes. I checked the output.log and did not see anything that needed a special attention.

Result=nothing changed on my landscape painting window and whole landscape is black in 3d view

I tried painting but some material do show up, some don’t and some others just turn the whole section gray.

Just now I updated to 5.1.1 but nothing changed.

By the way, did I loose all the painting I did before this happened?

I installed UE4.27 and recreated my landscape with the heightmap I have and created my landscape material + their layer info. But, I have the same problem with a different game engine??? What am I doing wrong?

I did not use the same project file as the one from UE5. I created a new one specifically for 4.27

The only common denominator are the textures. I created them with Gimp and exported them as 8 bit PNG files with no Alpha channel.