If you move within range of the Pokemon, and leave the range before it shows up (there is 10 seconds between showing) it will disappear from the radar, and not show up again until the next 10 seconds.

I have tried hard, even been annoyed by people always complaining about tracking. But it is totally undoable right now.

Having to go 300m away from the Pokemon before it disappears, and you would have too move pretty much exactly in 70M increments pausing for 10 seconds.

Say you just had to walk 150m before it disappeared, and you ran right towards it. You would have to 70m away in under 10 seconds. Wait 10 seconds. Walk 70m away, wait 10 seconds. See it disappeared. Walk the 150 Meters back. Wait 10 seconds. Walk 70 Meters in 10 seconds, wait 10 seconds. Walk 70 Meters in 10 seconds, wait 10 seconds. Walk 70 Meters in 10 seconds, wait 10 seconds. Walk 70 Meters in 10 seconds, wait 10 seconds and it shows up or it would disappear and you then need choose one direction. The whole time you would need to move exactly between 7-12m/s. Because you backtracked you would probably get almost no progress shown on your buddy/egg.