I have this file (attached) which I can't thicken from some reason. Using the "thicken" command produces various errors along the lines of "failed to offset or face could not be deleted"... but it's a pretty clean file; not sure what's Solidworks problems. I tried looking at similar "thicken" issues people had but it seems people have very case-specific problems and I couldn't make associations to my part. Can anyone tell me what's wrong with my part-- why can't I thicken it?

It's Solidworks 2020; also uploaded as STEP file.

-Val