Why?

Has anyone else had issues with the day 50 siege achievement not unlocking? I just got all the way through day 52 without unlocking it.

First of all, the new siege mode is very fun, I recently bought the new expansion and just got the day 50 achievement. One thing I noticed in later days when there are a lot of towers on the field, playing on 4x speed sometimes caused enemies with empty HP bars to not die, they keep moving with empty HP bars. When changing the speed back to 1x they die immediately. I'm playing with low performance mode enabled, screen shake and tower recoil disabled for best performance but it still gets quite laggy when ...

1) Negotiator doesn't eliminate enemies upon closing the gate. 2) I've occasionally encountered game speed getting set to 0 upon opening the gate. This happened to me the first time I played, and I was very confused about what I was supposed to do next. 3) Getting off the ground in Siege feels awfully hard, at least at low Siege levels. 3) Nebula is ridiculously good, and getting one in the first pack I opened in a run hard-carried me to day 15, after previously having failed to get past day 2 or 3. 4...

Am I correct in thinking the following is all true about the Electric Banshee? 1) It is unaffected by range modifications. 2) It is affected by rate-of-fire modifications. 3) Its "Wave Start: Deactivate 1/3/9 towers" selects a random tower on the map and attempts to deactivate it, rather than selecting a random deactivatable tower to deactivate? That means that it can fail to deactivate any towers if you have more than one Electric Banshee, or an EMP Wall on the map (even if no other towers are ...