Reactivating a user and getting "group with primary key value is "null" not found" pop-up

[MPH2]

I have a user who was assigned an External user role in Workfront. I don't know when this happened, but when I went to update their account, it wouldn't let me save any changes to it. I have run into a similar issue and my resolution was to deactivate the account, make the changes, save the account, and then reactivate. Up until now, that's never been an issue. However, today, I have this pop-up: "group with primary key value is "null" not found" come up when I try to reactivate this user's account. I'm the sys admin, so I should be able to make these sorts of changes without issue, but that seems to not be the case this time. We use a SSO login, and when I look at their account on the Admin Console, they have a Federated ID (as they should), so everything looks like it should be good to go. Is there something I can do to resolve this from my side, or is there something I am overlooking?

[MPH2]

To add, I removed their license for Workfront in the Admin Console, saved it, and after a few moments re-added the license and their account on Workfront was automatically updated. However, I am still unable to make any changes to their account and I am not able to locate their account when I go to the Log In As option in the Setup menu. I am exceedingly confused...

[KatherineLa]

The External User access level doesn't work with Log In As, so that's part of your mystery. That access level can't actually 'log in' to Workfront themselves, they just view what has been shared to them.https://experienceleague.adobe.com/en/docs/workfront/using/administration-and-setup/add-users/legacy...

As far as the error message, I've run into that a few times when trying to use the 'Reactivate User' menu option, but I'm able to simply edit the user's profile and re-check the Active box instead, select their access level and home group etc. Done that way, it's saved for me.