Did you change the security role when you reverted to TCP?
Applications > Application Types > WebSphere enterprise applications > IBM Lotus SIP Registrar > Security role to user/group mapping
Ensure AllAuthenticatedUsers is set to Everyone in Application's Realm.
Check out
https://www.ibm.com/support/knowledgecenter/SSKTXQ_9.0.0/admin/secure/sec_av_transport_tcp.html for more info