Admin UI causes search builder (not form builder) to crash
I think it's from here: https://github.com/civicrm/civicrm-core/commit/db712b3108970b3560488928c85d8f0343016603#diff-191c3573321ff5ab86bbe647462fbdbfbf3779611ec18a4aef86ec1a638d0043R5, which conflicts with the url civicrm/contact/search/builder?reset=1
While technically a regression, given that it's been stated search builder is not officially supported and was removed from the menu for new sites, I think the todo is to give a heads up somehow that in 5.64 search builder will stop working if you enable admin UI.