We ran 16 man last night without issue until the puzzle boss. Something had to be off with the spawns because it felt like nightmare mode +. Within 10 seconds of starting we had two spawns of elite mobs. By the time we had the bottom teir solved we had 9-12 elite mobs.
Like you, after about 6 failed attempts we split into two 8 man groups and had no issues. Puzzle boss was uber easy on 8 man.
We did run into issues again on SOA. We had several bugs there, most notably the random despawn and reset below 10%. We were trying to figure out if we caused this somehow. What we noticed was the tank would get him below the falling pillar and his shield would come down once. On the second pillar or third he was directly under it but the shield wouldn't go down and he would instead de-spawn and reset shortly after.
Frustrating to say the least. We would have cleared 16 man in about 2-3 hours without bugs.