You probably forgot the 5Nd

Your shares are reward for the 5Nd after you submit them, so they wont get all their reward immediately.

If you look at the Rewards page it will tell you the block's 5Nd range (431hr 40m 3s = ~18 days) and what your average hash rate was over that ~18 days.
e.g. if you mined for only 9 days, then you'd get about half.

Everything keeps getting paid, so it's not like you lost the other half, it's just that the shares get reward for 5Nd from when you submit them, (usually) multiple times, expected on average 5 times if luck is 100%.