Audio Units/Plugins not functioning

Hello all you nice people!

Having a devil of a time with this. For some reason, even though I can add Logic amplifiers and/or Amplitube amps or any other effect plugin for that matter to a channel strip they don't engage. I hear the unprocessed guitar tone but the plugins don't work. I'm running the latest version of Logic (11.1), the latest Mac OS (15.11), a brand new Focusrite Clarett+ 4Pre interface on a Mac mini 3.2Ghz 6-Core Intel Core i7). I switched back to my 1st Gen Scarlett 18i8 and the issue persists. I contacted Focusrite support and we went through all the troubleshooting steps and concluded the issue lies with Logic. Creating a new Logic project does not help. Uninstalling and reinstalling Logic does not help.

Any assistance is greatly appreciated!

~tf