Are the problematic plugins in VST2.4 or VST3 format?
In Windows Explorer navigate to the following directory:
C:\Users\<user>\AppData\Roaming\Blackmagic Design\DaVinci Resolve\Preferences\Fairlight\Effects\
Rename the FXConfiguration.xml file (e.g. FXConfiguration_backup.xml) and then restart Resolve in order to rescan all plugins.
Are all plugins scanned successfully and loading correctly?
Include both the new FXConfiguration.xml and FXConfiguration_backup.xml files in this thread to assist the developers.