I just started a fresh 5.5.2 project and this problem is still there, have to reset the asset pipeline every time or it tries to overwrite the first FBX or if its in a different folder, it will take on the name of the first FBX, doesn’t seem to matter if its a static mesh, or a skeletal mesh, it makes unreal 5.5 unusable.
Typing this into the console works though, Interchange.FeatureFlags.Import.FBX 0 bacially turning off that new feature thats doesn’t work.
Just to add, I ran into this issue after upgrading from a 5.4 project to a 5.5.1 project and it still persists when upgrading that project to 5.5.2. I cannot reproduce it in a new project using the same simple assets that cause the issue for me in my main project. Resetting the import pipeline resolves the issue for now, but I had to do this a few months ago right after the 5.5.1 upgrade and it started happening again even before I upgraded to 5.5.2.
Just to say I was also having this issue and banging my head against the wall with it. I just tried resetting everything back to default on the importer pop up and this has worked for me. I was getting this using a Blender to UE addon as well as manual export of an .fbx.
I ran into this issue today too and was pulling my hair out thinking it was a problem with my mass-export from blender. Thankfully I stumbled onto this thread because searching for a solution is a nightmare.
I can verify that resetting pipeline settings on the importer popup solves the issue.
UE 5.5.3