That thing with Pokemon on the Sightings dissappearing isn't caused by the gps or your phone it's 100% down to the game, don't forget also now that Pokemon on the nearby are no longer unique... as in if you look at it you would only ever see the 1 Pidgey even if there is 20 within the 200square meters around you, only the closest one will show up, often the dissappear reappear is when a Pokemon on there has timed out, allowing another one of the same type to appear on your nearby instead, if you also only ever use this sightings to try to find something it is just not fit for purpose because of the way it works.

Say if you have

(West) Pidgey 50m - Weedle 25m - Eevee 20m - You - Pidgey 10m - Eevee 25m (East)

Obviously on the nearby you are going to see a Pidgey as the closest thing to you, but if you move in the direction of West you will encounter an Eevee before the pidgey, but when you get to that Eevee and catch it, the Sightings will update and place another Eevee near you... but now in the No3 position because you are moving away from it, so you might think that because you were moving one direction and encountered a Eevee which would have been the 2nd closest thing to you, it would make sense that for there to now be another Eevee in that same spot behind a Weedle which you would be in range of seeing, it only makes sense that he would be further West... even though that will take you away from it.

That of course is just the flaws if the world was 2d... which it isn't chances are there is going to be Pokemon on adjacent streets which will always be interfering with trying to apply logic to the Sightings system in game, which just means the best way to find stuff in PoGo is just to wander aimlessly and as quickly as possible, so it looks like you are basically strangest hobo in the world in a rush to get somewhere.

Also people talking about Rhyhorns being rare.... I've seen 1  in 500+ KM of walking with PoGo.

Well, I'm glad it's not my phone then, and I didn't even notice they stacked multiples of the same pokemon together. I wish they would at least seperate them, so you get a clearer picture on what is nearby you. The way you explained it, the current system Pokemon Go has is a mess. It's shocking I've been able to find certain rare pokemon that show up on my nearby list. At this rate, I've learned where all the spawn points are for pokemon, so I've been able to figure out where certain pokemon are hiding. Still frustrating though.

And I forgot to list Rhyhorn under my'uncommon' list. I find them sometimes when I'm going around town, enough to have one strong Rhydon on my team.

Dang, you get some pretty cool pokemon. I wish I could find poliwag, jigglypuff, ghastly and koffing more often.

Dang, well isn't that nice. I'd love to have that many pokemon appear around me. Even your avatar looks happy. I could use more stardust. And that's a nice variety of pokemon too.