I'm getting an odd behavior when using a developer account of type Admin in the web dashboard (the Owner account works fine). I can log in using this account, but if I select the account menu at the top right -- and maybe before that, actually -- I get a 401 unauthorized on the browser console and I'm logged out. This happens both when logged in as a developer on clover and when logged into the sandbox.
There is currently no ETA on when a fix will be implemented, but in the meantime, a workaround you can do is add your developer admin account as an employee of the test merchant account you are trying to view. You just need to use the same email you used for the developer admin account for the employee email. That will give you the permission to view that test merchant.