Samsung Galaxy, Android 10

Yesterday everything in WhatsApp was normal. This morning I see several (about 20) of my conversations in WA have no name attached, just the number. I look in my phone contacts and those people are listed, but they don't have the "Message/call via WhatsApp" options any more. Also they don't appear in the WA contacts list.

However, I can still WA message the people that I have conversation histories for, even though they're not in the WA contacts list.

I didn't change any settings in my phone since yesterday. Maybe some database error at WA? Connected with the new T&Cs perhaps?

Whose phonebook? I didn't change any setting in my phonebook.

The only app that was updated was Google.