Administritor Role assignment on Azure Portal can not choose Scope Type for Service Principal

Question

We are currently having problem with Role assignment in our Azure AD
logging one of azure administrator account,
The "Scope Type" field was grey (have tried Application Administrator, Cloud Application Administrator, Privileged Role Administrator, Exchange Administrator etc),
and we could not access any of our Applications (Service Principal) to use as the target of these assignments

normally, I think should choose scope as "service principal", then search particular service principal name to be member.

and as below the "resource type" field is showing "loading..."
It seems to be a permission issue of this account, but I wonder where I need to check, thanks.

This was possible before (a week ago) and done from the same account as
evidenced by these mentioned roles appearing on the page.

Answer 1

Update:

After two days, I found the Service Principal could be searched out from the "Select a member" at right side again,
even the Resource Type is still loading, the Scope Type still can not be changed, Directory as default.

But still didn't figured out why, is that because of Account permission or Azure Portal issue?