It's in the temp folders so that's likely why, you can do the same steps and look at the folder again and it should be there
I'll probably improve the logging since the error window doesn't display all the information, the app doesn't generate any logs when compiling which I should add in for 1.2 so it's easier to troubleshoot issues
While vertex issue isn't a bug with the application as you'd know, I could probably try to find a way to allow models like these to be compiled by adding in more files, though I'd need to check the docs again
While I haven't found the exact cause of it, I looked at the file and noticed that the GLTF file is exporting the vertices for every face that needs to be connected and as such the vertex count is going up a lot while the FBX just has the vertices connected normally,if you import the meshes and then select a face and move them and compare how it is for the two models you will understand what I mean