Unable to join sites to a Hub - Attempted to perform an unauthorized operation

I was able to associate sites to our Hub sites we had setup and life was good.

But then around a month ago it just stopped allowing me to join any sites to any of our Hubs. I now get the error: "Attempted to perform an unauthorized operation". Others in the company have no issues - just my account.

I'm a Hub Owner, Site Collection Administrator, and Owner of the Hub sites.

I'm a Site Collection Administrator and Owner of the sites I'm trying to associate.

As mentioned this was all working fine - then one day it just wouldn't work on any of them. Been like this for a couple of months now and still can't resolve it. I created a new Hub site and same issue.

I've cleared caches, tried different browsers, rebooted, logged out/in of my Office 365 Profile, cleared credential manager, etc. and still the same issue.

I was also able to rename Hub Names before where I was a Hub Owner, but now get the exact same error: "Attempted to perform an unauthorized operation". Both issues started at the same time so very likely related.

Note that I'm using the SharePoint UI (Site information > Hub site association) to try and associate sites.

Any help would be much appreciated.