Happened twice to me today.  Got the message : " You can't reach that". Animal was branded so there shouldn't have been an issue in the first place.  Had some cotton in the saddlebags and couldn't reach it, tested on Epic and Deliverance.  Only way to get the items from saddlebags implied unequipping saddle from animal.    or   Having the animal tame.   Seems that the option to "unequip all" also disappeared in the process. Creature was branded.