From what Psykin is talking about:
It's animation stop from white skill spam that's actually causing this.
For the plant scenario, other team's plant used white, then moon shaman bro etc... proceed to rip continuous whites after a little ramp up, not giving plant soul time to release from the white guard and go back to targettable. In cases where you can turn auto mode off, this isn't as bad since it only takes a momentary break, but for Coli/Pit, this can be a problem.
As to the shaman stun, I'd speculate a similar situation. I'm guessing that heroes have a momentary immunity period when either going into or coming out of the stun, and the white spam circus is catching it at that moment.
All in all, I'd wager the problem isn't likely to be shaman's stun, but rather animation stopping from so many back to back white skills going off.
The 2 examples I grabbed aren't quite total lockout, since I couldn't manufacture it with anything in the Pit that I could attack within 10 tries or so, but it demonstrates the rough sketch of the problem.