Hey @matthu
Probably try the following.
Pre: Close all tabs and start fresh
Step 1: Open the Portal app in Portal studio
Step 2: Try Sync config and browse the website > Ctrl + F5
Step 3: Once it is loaded then append the following URL string and hit enter
https://yourpotal.powerappsportals.com/?powerportal-designer.enableMultiTenancy=false&powerportals-common.enableMultiTenancy=false
4. Once it is refreshed. Then go back to make.powerapps.com then load the Portal management app.
Hope it helps.
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