My quick answer would be that weather changed (to partially cloudy) and triggered a new pokemon. You said that it was still cloudy, though. Sometimes weather icon takes a couple of minutes to update and display on the screen. That's the only logical explanation I come up with. Otherwise it's a very odd situation.
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Spawn question
So, living at my house for some time now, I've figured out the spawn pattern. At 42 minutes after the hour, something spawns in my driveway. It's there until 12 minutes after the next hour, and then vanishes. Next hour, at 42 past, another spawn.
So, coming home from walking the dog tonight, around 8:50, I catch the weather buffed Bellsprout (cloudy) that spawned while I was out. Nothing newsworthy there. Then, right at 9:00, a Taillow spawns in the same spot. The weather is still cloudy. I've never seen that kind of double spawn there before.
Thoughts?
P.S. - Yes, it is nice having hourly spawns at my house. But we're moving at the end of July, so I hope it doesn't derail my dust grinding (unless the new house also has a spawn point at it, of course).
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Answers
There are 2 types of spawn points, the majority are 30 min points but some are 60 min points. Each point spawn 1 Pokemon per hour, always at the same time after the hour, but different from point to point. The 30 min points will spawn a Pokemon for 30 mins, and then there will be a 30 min gap without a Pokemon. The 60 min will spawn for 60 mins and soon after despawn a new Pokemon will spawn, so these points are always occupied.
If you follow when your spawn points spawn and despawn you will see the pattern.
I have 3 spawn points I can get to from my house, and I know that there is a 10 min window every hour that all of them are active and I can get all 3.
I know spawn points are predictable and the situation described above is odd. But I've seen before what looks like 2 pokemon at the same spot after a weather change. And there's the known issue of not being able to click on a pokemon after weather changed. That's why I suggested that possibility. It may be just a bug as you say, though.
