Sacrifice at Dusk 5 times in a row

Hi.

Recently I started getting only Sacrifice at Dusk drops from Vaal Vessels. According to PoE wiki the chance of Sacrifice at Dusk drop from Vaal Vessel is 20%, so getting it 5 times in a row, which happened to me is 0.032%, which seems too low to me not to consider this as some sort of a bug. Is there some sort of limit to the ammount of Vaal gems you can get, after which only Vaal fragments drop?

Please let me know if this is a known issue, or if I should submit some sort of bug report.
Thank you in advance.

It's random. There is no bug.