Contact in iMessage only shows number, but no name; their info is in my contacts.

I have a contact whom I have texted before on my iPhone using iMessage. They are in my contacts under their name. What is weird though, that just seemed to show up was their text thread now only shows as their phone number and not their name even though their contact information is on my phone. Any idea why this could be?

I don't want to text the number if by chance this individual changed numbers or what. Could that be the reason or maybe they blocked me! haha.