LDAP login into F5 interface takes 30seconds or more

Like the subject says- we're seeing logins take 30 seconds or more when trying to login to the F5 interface with LDAP enabled.

Using port 389.

Directory service: Windows AD LDAP -

The only thing I can think of is that we have UDP blocked and it appears UDP attempts to use UDP before it times out and uses TCP.

Anyone else have experience with this?