When you use Install Plug-In File to update an existing plugin, Get ( InstalledFMPlugins ) immediately reports the new version installed, while the plugin version actually loaded still seems to be the pre-existing version.
This can easiest be seen by comparing each plug-in's own Version function with the version reported by Get ( InstalledFMPlugins ).
However, since the plug-in running is actually the old versions, any new functions will also be missing, and changed functions will actually not have those changes.
Get ( InstalledFMPlugins ) can therefore not be relied on for controls before executing plug-in functions.
It is only after restarting FileMaker Pro Advanced that the updated version actually is fully installed and in use.
The attached file (macOS only) illustrates the issue using the MBS and BaseElements plug-ins (2 versions of each included - hence the large file).
The 2 first records are before restarting FMPA, the 3rd record after restarting FMPA.