Bulk renames of users through LDAP becomes increasingly slow

Issue Summary

When renaming a bunch of users, such as when changing the username attribute of an LDAP directory, the renames start off fast, but become slower as time goes on.

Steps to Reproduce

1. Sync an LDAP server with a lot of users
2. Change the username field

Expected Results

Users are renamed and each user rename takes roughly around the same time

Actual Results

User rename duration increases over time, meaning that migrating a lot of users becomes very slow.

Workaround

Currently there is no known workaround for this behavior. A workaround will be added here when available