As part of VMSA fixed patches, changes were made to further secure the vCenter Server plugin architecture. This may have a negative effect on some third-party plugins that were not authenticating correctly. Request you to check with the vendor that supplied the plugin if you are facing any issues with 3rd party plugin post patching to the latest vCenter Server patch.
This is also documented in VMSA-2021-0010 Public FAQ :
https://core.vmware.com/resource/vmsa-2021-0010-faq - "I have a third-party plugin installed and after the update it does not function anymore. What should I do?"