The "9.91" in the filename is the protagonist's fatal flaw. If you update your Waves Central software to a newer version (like V12 or V14) but kept your old V9 licenses, the new "Shell" might overwrite the old one. Suddenly, your old projects won't open because they are looking for the version 9.91 shell specifically.
You cannot manually install or update Waveshell2-vst3 9.91-x64 by downloading it from a third-party website. Legitimate updates only occur through —Waves’ official license and installation manager. Vst Plugin Waveshell2-vst3 9.91-x64 -vst3-
Every part of this filename has a specific meaning: The "9