I had a quick look and I think you actually found a bug.
I did a quick test with a model here. It has 4 materials. I changed one of them so that it became the same as another one. After that the material list shows 3 materials. But if I change that material that is used on 2 parts now, only one...
I would check the material settings. Since you see the shadow and normals, maybe the material is fully transparent?
If you swtich from textured to coloured render mode, do you then see the polygons?
Did you have a look at the batch convert wizard in MCX already? I can help you to make certain changes to a lot of models at the same time.
When working on a library you can also just load the BGL file in MCX and then save the BGL file again after making the changes. No need to save each...
The red cross is the reference point of your object and the pink box the bounding box. If they are far apart that is typically not really good. You can best go to the move tool in MCX and center the object there. That will put the reference point in the middle of the bounding box.
Autogen buildings are rectangular, so the scripts filters out weird shapes that are not rectangular or can be split in a few rectangles. You could tune those rules a bit.
If you look at the log file you get an idea how many are filtered out.
Your script doesn't look too bad if you want something that works on any area of the world based on OSM data. It has some steps in there that are not really used, so you can simplify it a bit more:
You have a recent version, so that's good. It's weird that OSM works for me though.
This is an error from the webserver where the map data comes from, it will not prevent MCX from working, but of course it means you have no map to do the placement on. I'll double check if I can reproduce...
I did a little more search and found this thread:
There it is reported that the issue has been fixed in the Windows 1903 update. Do you have this...
Please check if you are using version 1.4 (https://www.scenerydesign.org/development-releases/ ).
There is no need to download things, the maps are streamed from the internet. What is the exact error message you get?