Try a couple of things:
1. "COMMAND-T" to open the symbol and see if it shows up in the 3D preview
2. Open the symbol and see if it shows up in the symbols 3D window
If those are OK
3. See if it's being excluded by the renovation filter - or -
4. DOCUMENT > PARTIAL STRUCTURE DISPLAY
It's frustrating but there will be a logical reason somewhere!!
Good luck.
PS - Edit your signature so your software / hardware details appear. It helps...
Cameron Hestler, Architect
Archicad 27 / Mac Studio M1 Max - 32 GB / LG24" Monitors / 14.5 Sonoma