Error: There is no connected account for the user a_second_user. Feed will not update.

Error: There is no connected account for the user a_third_user. Feed will not update.

Error: Access Token for cella.oak is not valid or has expired. Feed will not update.

There's an issue with the Instagram Access Token that you are using. Please obtain a new Access Token on the plugin's Settings page.
If you continue to have an issue with your Access Token then please see this FAQ for more information.