Howcome pools throttle the hell outta my shares always just before reaching around 300 accepted?

[2017-10-20 23:34:53] accepted: 291/291 (diff 1.619), 1604.02 Sol/s yes!
[2017-10-20 23:34:53] accepted: 292/292 (diff 1.836), 1604.02 Sol/s yes!
[2017-10-20 23:34:53] Stratum difficulty set to 63.999
[2017-10-20 23:34:53] accepted: 293/293 (diff 4.244), 1604.02 Sol/s yes!
[2017-10-20 23:34:55] GPU #2: Gigabyte GTX 1080 Ti, 564.58 Sol/s
[2017-10-20 23:34:55] accepted: 294/294 (diff 144.520), 1604.02 Sol/s yes!
[2017-10-20 23:35:21] GPU #1: ASUS GTX 1080, 402.13 Sol/s
[2017-10-20 23:35:28] GPU #2: Gigabyte GTX 1080 Ti, 607.58 Sol/s
[2017-10-20 23:35:28] accepted: 295/295 (diff 107.029), 1604.22 Sol/s yes!
[2017-10-20 23:35:29] accepted: 296/296 (diff 107.029), 1604.22 Sol/s yes!
[2017-10-20 23:35:29] accepted: slow as fuck (diff high as fuck), 1604.22 Sol/s NO!

It takes about 10 seconds to get to 292 then they go at a snails pace?

Someone please explain, coz I probably just don't quite understand how it works (other than the pool jacking up the difficulty on me 'coz it see's me rockin' it   )

This always happens on any of the algo's i've tried lately. Equi, Lyra2v2, Keccak etc.