so the "decreasing" performance
is was just a stupid bug in the counter or to be more precise, like i mentioned before, the col/min & sh/min counter was not reset properly on a connection loss
i fixed that with the last github commit, i'll update the windows binary in a few minutes
if your miner states ~1400 shares and the last blocks contains less than that, then the submission didnt reach the server
/edit1:OR
the only thing i can image of is that the pool software crashed sending some of the shares of the current round into nirvana (for all users)

let me check the time of the last restart of the pool software
(this should also be the cause of your connection loss &
buggy col/min+sh/min reset)
- xolokram