STEP file not working in Fusion?

Hi - Trying to work on an idea for a modification of just part of the original Expansion card housing, and I can’t get the STEP files to open in Fusion. I re-downloaded in case things had been corrupted (which is what Fusion thinks) or something had been updated. Anyone have any idea what is up with this? Does Fusion360 work for others for modifying the original card designs?

I’ve used Fusion for all my designs, just in case you are doing something different to how I usually import, I import, convert to mesh and then scale 1/10 if it’s too big in that direction, if you would like I can send over a f3d file.

I’m sure I can import thru STL, but it shouldn’t have to go through a mesh format. It should import as STEP so you can avoid that loss of precision.