[iMore Question]

Have tried sync with replace of calendar and contacts but items still missing.
Tried restoring phone with same results.

[xMatter]

Which service are you syncing from?

For instance, my primary email is an MS email. But when I would sync contacts and reminders, birthdays for contacts would be off a few days and not all contacts would sync.

I have since switched to an iCloud email so I know syncing would be correct 99.9% of the time.

[Rob Phillips]

Have tried sync with replace of calendar and contacts but items still missing.
Tried restoring phone with same results.

Welcome to iMore! Assuming you're using iCloud for your contacts, check out this Apple Support article. It should give you some ideas.
https://support.apple.com/en-us/HT204150