My wild guess is that your miners hashrate is so low that even to the smallest static difficulty (which is 0.016 like Lucazane said literally 3 posts above) causes your sharerate go way more down than what it was with previous minimum sharediff, 0.008. With my secondary card, GTX 960, this is the case and now I have to mine with it at Skein-pools, since I get about half of its miners reported hashrate if using Groestl with the current minimum sharediff.

As numbers, it's miner reports about 30-31MH/s, with earlier static diff (0.010) pool showed most usually 23-30MH/s and nowadays with 0.016 or higher an average of 16MH/s.

Other possibility is that you haven't updated your miner configuration of the static difficulty if you're using it, since as example on my case - I've got pretty unstable hashrates on pool as well if using automated vardiff since it seems to put pretty aggressively the diff so high that the actual results suffer pretty heavily at overall.

On my 1080Ti I've used fixed diff of 0.05, and the hashrate on pool is shown within 5% of difference at max compared to miners reported hashrate so it has worked on me.

But on the other hand; reading by what Lucazane wrote, the minimum sharediff had to be raised due to way too high constraint on server (resulting to the hard crash most likely), I totally understand his point. Too small miners and bigger miners with way too low fixed sharediff easily congest the server to it's knees instead of helping efficiently to find those blocks.