@masklayer Does it happen when sliced by software like the packages from https://www.flashforge.com/download-center ?
My guess is the geometry isn't being interpreted properly, and you already mentioned it's not a separate model. So it's probably something with how the mesh is set up or one of their fixups (min wall thickness, etc) breaking it.
Also maybe ask support, though last time I did, their turnaround was in the 24-48h range.
@masklayer I also recall their old UI showing warnings when those fixups break stuff, so it'd be really weird if one of those isn't raising here.