Hey Lora!
This is most likely related to a recent bug fix that changed how auto-created contacts can be displayed.
Previously, some auto-created contacts were being incorrectly shown to teammates even when contact permissions should have restricted them. The fix corrected this, which means some teammates may now lose visibility of contacts they previously saw.
This can directly affect things like contact suggestion in the composer. The teammates who are unable to see contacts are all members of a teammate group that does not have contact permissions. You'll need to update any teammate groups that do not have permissions to access contacts, and grant that permission.
We have an article here in our Help Center with more info on editing teammate groups: Teammate groups