Found clues. There is a lightmass imptance volume size 8000 x 5000 x 3000, covers whole level, uses all default settings.
Test this level by using Development package, fps is 80+. But fps is only 18 if used Shipping package, on same PC.
Test both packages on other PCs (different hardwares), result is same - mass fps dropped when using Shipping package.
After change the lightmass importance volume’s size ( scale to 0.5 x 1 x 0.125 ), we found the shipping package raised fps to 200+.
So, can Epic give us a clear explain why on earth happened behind the scene? or give us some guide to avoid such a strange issue?