So, I was getting increasingly frustrated with how it seems that sometimes I would block and sometimes I would get sheared in half and sometimes I'd be stunned when I blocked and sometimes I could counterattack immediately, so I decided that instead of getting pissed off even more I would experiment and find the pattern.

This bug happened to me on level 1 in chapter 1, insane difficulty. I was seeing why I could counterattack sometimes and why I couldn't and etc. when I found that sometimes when I block a sword strike it would completely prevent me from attacking at all, even after I recovered. I would run around for many seconds after blocking spamming left click with my character doing nothing. After a bit of testing, it seems that this happens EVERY TIME I dash with the "primitive" jetpack while in the stun animation.

Summary of the steps I believe that create the problem: Get stunned while blocking, use jetpack without jetpack upgrade, then you should be attack frozen.