G Suite - Domain whitelist but one school is blocked from adding files

[TwistedHelixis]

I have setup domain whitelist between 2 schools so they can create and share a team drive.

 

I added the other schools domain to the whitelist in both G Suite admin panels

 

I created 2 Team Drives, one was created in each domain and then shared to the other (using my accounts to share)

 

The first Team Drive works fine, I can upload a test file from both domains, but the second team drive I can only upload a file from the domain that created the team drive. When I try to upload a file from the other domain I just get 'Failed to upload' displayed for a second.

 

Obviously I have looked at the Drive sharing options, but nothing is jumping out at me that might cause this issue.

 

Anyone got any pointers?