@Mikhail Firsov
Hi,Michael.
I noticed that you mentioned you are using Exchange 2019 in the former post.
And I tested in my lab (both in Exchange 2019 CU2 and Exchange 2016 CU13) and got the same result.
The problem may be resulted from the distribution group not being resolved correctly into the mailbox addresses of members in this group.
As the error message statued "You don't have sufficient permissions to search the mailbox..."(while actually it's a distribution group) and accroding to this article from Exchange Team Blog.
I suppose that it may be a bug.
As a workaround,you can try manually selecting all specific mailboxes in the distribution group instead of selecting the distribution group directly.
In my test,the search can complete without the permission error.
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