Their soul recall only work half the time. Double pressing Q puts the ability on cooldown, and the charge remains. Fix
I have experienced this as well. Making them disengage the enemy just before using the ability seems to make the problem less likely to occur.
I've been experiencing this since the launch. I thought it was addressed when they've fixed stucking Jain Zar on Leap (and never mentioned it in patchnotes), but it seems it only became less severe.
One of the most annoying bugs currently, considering how long cooldown is.