I have a Nexus 5 smartphone with Andoid version 6.0.1

If I send a text message with Messenger (not Facebook messenger) and use a person's name in my contact list this message is received by the contact. If I start a new conversation and enter only that same contact's phone number, that message is never received. Is there a specific reason for this happening?

Any help in resolving this problem would be greatly appreciated.

Brian