I have a SOLIDWORKS assembly that I have been unable to save for a few days in 3D PDF (the pc pedals and reports me an "error" 50/330 etc.) while everything worked well previously and it still works for other files, moreover the drawing extracted from this assembly can no longer be saved as a PDF either.
Transforming into a room can indeed be a good solution.
However, be careful to check the hidden elements, deleted, etc. which can interfere with the conversion (in addition to making the PC grind for nothing).
If the assembly is not very big and it is not confidential, it is possible to post it here so that we can try it on our own.