when i pin a contact in messages it goes back to unpined when i close the app

Hi airdrop162,

Thank you for participating in the Apple Support Communities. We understand when you close the Messages app your pinned conversations become unpinned. You'll want to make sure you're following these steps to pin a conversation: Keep track of conversations in Messages on iPhone - Apple Support.

"Pin a conversation

You can pin specific conversations to the top of the Messages list so the people you contact most always come first in the list.

Do any of the following:

• Swipe right on a conversation, then tap .
• Touch and hold a conversation, then drag it to the top of the list."

If the issue persists, try restarting your iPhone to refresh iOS and apps. Also, we recommend updating to the latest version of iOS to see if the issue persists after doing so. Here's how if needed: Update your iPhone or iPad - Apple Support.

Take care.