Authentication issue in designer with multiple user sources

We have two user sources: Microsoft Active Directory (main) and 'default'. I have the same username in both, but in 'default', I have the 'Administrator' role.

I have a parent project, with many children, and they all stopped working recently. The Perspective pages load, but it's as if they can't access the inherited resources from this parent, leading to a mostly blank screen with this error:

The parent project has always been set to the 'default' user source, in which I have the proper roles that match those configured in Project Properties -> Permissions. However, once this issue started, I found that I can't open this parent project in the designer at all due to lack of permissions:

Here is the configuration for the parent project:

It looks like the designer is trying to authenticate to the AD instead of the default user source, or something like that. I poked around quite a bit in the gateway server files to see if I can modify a json somewhere, but I did not find anything promising.

I have a couple of ideas on how to get the permissions modified and get these projects back up and running, but I'm hoping for feedback on which route is the best to take. No matter what I do, I need to wait until production is not running, so I have time to plan out my moves.

My first idea: One inherited project does have overridden permissions settings, and I can open this in the designer. My first idea is to open this project, click 'export', and select the Global Props only and then 'Send to' the parent project.

My next idea has a much bigger blast radius: Take an export of the whole gateway, delete the AD user source, open the parent project, modify the permissions settings, export the project, restore the gateway using the backup (to restore the AD user source), then import the project (including its new permissions settings).

Another idea would be to just change the user source for the project in the gateway config (third screenshot above) to the Active Directory source, attempt to open the project in the designer, and then change it back -- maybe this will update some bad cache somewhere.

I haven't dealt with many permissions/user source issues in the past and want to minimize any potential issues while maximizing chances of success. Any ideas appreciated.