Thats weird, because its working for me on multiple themes, and servers….even local servers.
I did a search to see if other people had the same issue, and I saw some old posts on WP forums that said something about Permalinks structure, and hosting. Although I’m not sure if thats the case or not since most of the posts were old (5-6 years).
If you want to create a temporary login, I could take a quick look to see if I notice anything that could be causing the issue. If not, try deactivating plugins to see if anything is conflicting with this.