High level Oil drop rate is very very low

I don’t know it’s only me or GGG has made some changes on high level oil drop rate, but I feel like since 2 weeks ago, Cassisa encounter in normal map has very low drop rate for high level oils. It’s hard to see any oils higher than Crimson oil. As before, I could find silver or even golden oil in normal map Cassisa encounter. Did GGG make the change in one of the patch or it’s just unluck?

Thanks

it's just luck, I have seen all(and in multiples) of all but golden.