I keep rebuilding an assembly (v2020) and save it.

Every time I re-open it, three assemblies I add become, well, disassembled (I'm not sure what to call it).

Every...

Time...

Open, rebuild, save, close.

Open, rebuild, save, close.

Open, rebuild, save, close.

Open, rebuild, save, close.

I can't figure out what I might be doing wrong.

The assembly being added is a step file. (620161-8500-000_01-001_asm.stp)

When