Slow Bubble Bug?

This is my first error report, I'm not sure am I doing this right.
my report number is 1,762,212,537

Atfer killing several monster underground, I suddenly feels like my charactor's attack speed is being slowed with my crossbow. No debuff, no item change or passive change, no second set of weapon and nothing alive was next to me.

I try to move around and clicking attack button, nothing changed.

And then I keep on going and run into another group of monster, which included a slow bubble rare monster, I run into the bubble and I can tell my speed is totally the same as the moment before I got into the bubble, after running into the bubble and kill the rare monster, my speed has been fixed to normal.