I haven’t “seen” my pokemon for more than a year.
Do you have any pokemon in gyms on eternal defense? By eternal I mean a year at least. Here is my mighty lvl1 30 CP Blastoise: https://imgur.com/a/bjkuLhw
P.S.: Oh, and there is also Hoothoot with 200+ days in the same gym.
UPD: What is your max defense time? Share screenshots with your pokemon 😉