I’m testing the free version of Gaea.
I’ve exported the mesh, which is quite dense.
I’m getting this result (the material doesn’t make any difference, the jagged lines appear even with the default material)
I haven’t used Gaea, but It sounds like it had custom normals data. Next time try clearing that by going to Object data tab > Geometry data > clear custom split normals data.
I’m checking and in the Geometry Data the default option is add a Custom Split Normals Data. I guess it’s due to the way the geometry it’s being exported.