I need help, the model got flattened and mixed up when imported into blender and roblox studio

I need help!!
Hi, today I encountered a problem when importing a model. Unexpectedly, when I imported the model into Roblox Studio, it flattened and all the parts changed their location… everything was fine before. After that I checked the model in Blender, and everything was exactly the same as in Roblox Studio there. At first, everything was fine with the model 1, but I needed to change some details (I merged some layers and reduced the number of polygons and imported as the 2nd model) And after that this happened. Then I decided to export the file of the 1st model again and import it into Roblox Studio, and the same thing happened to it as to the second one

I have attached a screenshot comparing the second model with the very first import of the first model,screenshot of the model in nomad sculpt and screenshot of the 1st model in Roblox Studio after the second export from nomad sculpt