Does Gym defending pokemons automatically get kicked out for a specific condition without getting invaded?

I live in a small town where exists 6 Gyms and 18 Pokestops. Since a week I have been noticing that 2 of those 6 gyms are malfunctioning, or maybe I am wrong...

Now let's come to the main point...

So story of 5 days ago, I captured all of the 6 gyms. So today 4 of the 6 Pokemons got kicked out. Out of the 4 gyms from which my pokemons got kicked, 2 of the gyms are being controlled by another team and the rest of the 2 gyms are empty. For the rest of the 2 empty gyms, I doubt that had someone invaded it, he would have left his pokemon in it, but the rest 2 gyms remained empty .

Today is not the first time when those 2 out of 6 gyms malfunctioned it happened to me a couple of times

(Both of the malfunctioning gyms are newly transformed).

So, is it a gym glitch or someone is secretly invading the gym without leaving a pokemon to defend?

Or

Is it some unknown condition being met, the Pokemons are getting kicked out ?

Thank You!

Solution 1:

I can see if you are passing by in a bus you might just throw in a battle to kick the Pokemon out, but by the time it’s done, they are too far to put one in. I just don’t get why you would do so, waste the ressources without much benefit.

I went and checked and there is no 'upper time limit' on how much time a Pokemon can stay in a gym. There has been reports of gyms being held for up to 80-90 days. So it’s not that.

Other option is that some Pokestops were added to the area and what is a Pokestop/gym has been reshuffled. So it’s a gym that is at the same place, but is not the same exact point. But I think usually it will take a Pokestop and make it a gym, but not the other way around.