Yeah, Adobe tech support can really be frustrating. If the Adobe tech tells you it’s a plugin issue maybe ask them to download the plugin themselves and test the install on their computer. Then they will see that the installer works.
If I knew what to look for then I would try to help…. but I just don’t. They really need to help you with it because the issue is on their end.
Another user on a windows computer had this issue recently and on their computer it is some type of user account issue where one user account on the computer will install and another won’t. I still have not heard back on what Adobe said about their computer. I couldn’t figure that one out either.
Being that you computer is Mac it may be a completely different issue than theirs but it sounds similar. My gut feeling says there is some type of security issue with Creative Cloud on certain accounts… but again I really don’t know.
If Adobe tech support tries to pass the buck then if you could get me the char dialog with the tech support rep names in the dialog, I will will report it to Adobe.