Based on your description, I guess this issue related to the Exchange RBAC permission (Other admin may modify/remove a part of your Exchange admin account permission). You could take the steps below to check it:
Check the migration request command contained in which admin group:
Then add those admin permission to your admin account:
It is the same as Exchange online:
Permission, I would suggest you create a new Exchange online and on-premises admin account, because your account may have other permissions lost (You can also add them back as above when you find any permission is lost).
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