Earthquake Attack Speed Bug When Dual Wielding

Basically, if i 1H the mjolnir, the attack speed on the skill "Earthquake" is consistent. Once i use Giant Blood and put 2H weapon as off-hand, the attack speed on "Earthquake" becomes so inconsistent that it affects my gameplay so much :(.

For example, it would hit as fast as it's supposed to be, which is around 0.8s. Then after casting "Earthquake" a few more times, suddenly the attack speed decrease above 1s, possibly double the actual attack speed.

I did a few more testing by opening the skill description to ensure that the "Attack Speed" stated in the description is constant, but the actual "Earthquake" still slows down sometimes.

I tested both in my hideout and during mappings, both gave the same result.

I have tried removing "Martial Tempo" from my "Earthquake" thinking that it could be my attack speed is faster than the shockwave from "Earthquake", but nothing happened too.