I had similar problems when, believing I had understood and mastered the technique of constructing the textures maps (normal, roughness, opacity, reflectance, environment ...) I "let go" to fill my models with all these textures , built on their own with gimp, with the belief of enriching the model of better features.
I soon realized that it was not all that easy and immediate ...
The appearance of shadows, reflections and unwanted transparency made me desist from the experiment.
Now, if I'm not sure, I prefer to use only the "diffuse" texture, and, usually, I have no problems.
I use the additional textures only if they already have a model that I find on the web and that, therefore, I consider already tested by its creator.
In this case too, however, the recommendations of the developers of Outerra should be implemented in carrying out the appropriate conversions.
Textures must be converted into "dds" format with these characteristics:
albedo: DXT1 format
normal: DXT5 format
roughness: BC4 / ATI1 format
opacity: BC4 / ATI1 format
reflectance: BC4 / ATI1 format
environment:DXT1 format (maybe not yet used)
and all accompanied by "mipmaps".
Another recommendation is to use textures with height and width values (in pixels) is multiple of four.
There should be no visualization problems, if you do not observe this last rule, but, surely, the speed and optimization of the renderig improves.
There are software that automatically create all the desired maps with excellent results (you can do a search on the web), but I have not found free programs and, as I am more interested in programming, for the moment I "postponed" this study and are not able to give advice.
( Just because I'm not very connoisseur of the topic, please anyone who has noticed that I gave inaccurate news, to correct me !)
I do not know if I have correctly interpreted your problem ...
I hope I was helpful.