""Pokemon has fled" on nearby tracker but still catchable?"

#PokemonGO: Maybe this is a known bug, the nearby tracker has only recently come to my country (Vietnam) and I didn't follow too closely when it was originally released as it did not affect me yet.Basically, I have seen several Pokemon that are semi rare in my city. I click them through so they are marked on my map. Then as I am proceeding to the pokestop occasionally I get a message that "the Pokemon has fled". The first couple times I forgot about it and changed back to my normal route. Then one day I continued to the stop anyway, and low and behold, there was the Pokemon! Since then this has happened 6 times all with semi rare Pokemon so I doubt there were simply two of them and no lures up. Any ideas? via /r/TheSilphRoad http://ift.tt/2hI8z0K