NC gets slow after switching to LDAP

NC 11.0.0 gets a lot slower after switching to LDAP users. Previously, the local users all can sync with the server. After switching all the local users to LDAP users, most of them can’t finish a complete sync with the server. There are about 40GB data on the server, and most users have access to a part of the server.

The LDAP server is running on the same server and using TCP socket to communicate with NC.

Any idea about this?