Shibboleth SP 2.5.4 Template Attribute Resolver: Unknown plugin type

[Cantor, Scott]

>       <Library path="plugins.so" fatal="false"/>  <-- I have also tried the full path
> name, but received the same result.  No message about failing to load the
> plugins.so in the logs

Basically impossible, that is the error, so you either didn't restart it or that isn't in the actual configuuration. If you're going to depend on it working you should flip the fatal flag anyway.

-- Scott