How do I restore missing contacts on my iPhone 12?

I have a iPhone 12; iOS 18.3.1. I have saved contacts that sync to iCloud and my Google account.

In the past a few contacts disappear from my address book and I’m left with numbers without names on my iMessages, call log, WhatsApp and such.

But recently it’s like a whole chunk of contacts have suddenly disappeared. And these are even contacts that I am in touch with frequently, so I don’t think it can be similar to the offload app feature.

Has anyone experienced anything similar? What could be happening? Is there a fix?

[Re-Titled by Moderator]