Sometimes settings or updates cause an account to become unlined from the platform. Please check to see if any profile settings have been updated on your Instagram settings, and then adjust if needed.
To confirm, go to Account Settings on the Instagram app. Confirm that 'Sharing to other apps' has your Facebook page linked to your Instagram account. You can also confirm settings by checking the Accounts Center in the Instagram app. Please confirm as well that your Account is a Business or Creator account.