right; so this only happens to specific contacts and every time?
And the contact's name shows in the message app when you open the app?
have you tried seeing what happens when the contact facetime's you or calls you?
Is the contact an apple contact using iMessage or using SMS ?
One of my next steps you won't like, but the contact names are derived from the conversation, and you might want to try deleting the conversation. If there's a corruption there it might be an issue.
Also worth trying setting a Nickname field on the contact and have your preferences use nickname as the display for conversations.
It's similar to mine issue but not quite the same. The phone might be failing to translate the conversation participant's name.
If they're on iMessage you could try to set up a group message with another contact, and *don't* set a title or topic or name for the group; and I think it lists the participants and see if they still show as a number or if that makes them show as a name at the same time as them showing as a number on the other conversation; that might imply a corruption on the conversation. But I've never worked on the iOS platform software so I'm only going on how I would link these things together. Messages won't have access to the contact, but it will have the number. If the conversation has somehow had the number set as the title then you'd expect to also see that showing in the messages app which I guess you would have mentioned if that was happening.
Can you ask siri for that contact info from the lock screen? I've had issues where I've asked for a contact's address and Siri just retorts: "I cannot access that information at this time".
Do you have Touch ID on?
If so can you set your notification preference for Messages to only show when unlocked, then when the message comes through just raise to wake and rest your thumb but don't press (and don't have the old style unlock switched on so it doesn't fully unlock it just removes the padlock) this will "reveal" the message but also make sure you're unlocked and have full API access to contacts.
I'd say the sequence of number's is less likely.
SMS or iMessage?
Facetime / call result?
Nickname on contact?
Group message?
Touch ID message reveal test?
