We have an application where every auction has a favourite and 'notify me' button (for when the auction is almost over). The 'notify me' button is linked to the favourite button, as in, you cannot unfavourite something if you have a notification active on the auction.
Once you remove the notification, you can also remove the favourite. The same issue is present when you bid on an auction; you automatically favourite it and cannot undo this until you are no longer the highest bidder. This leads to confusion regarding when you can and cannot interact with the favourite icon.
Currently we have a tooltip that tells the user the situation, but this obviously cannot work on mobile.