I have just encountered the bug. Surprised by the number of comments here confirming the existence of the bug and a staff member to pop in claiming they cannot reproduce it. Also, I fully agree with one of the replies here saying that they don't feel like playing this instance over and over just to get around a bug. It's disappointing. I have it on video as well, if a dev is interested. As per the solution, which happened during my second attempt. Originally, I did notice Tonn staying idle after the second tower, and I wondered if this is normal, but since it was the very first time I was playing this instance, I ignored it. When I realized that he was needed for the third tower, I went on Google to search and came across this thread.The solution I approached, thanks to the guidance from everyone in here: When I entered the instance, I talked to Tonn so that I get him to follow me. Then, I ran to the cave and did not actively engage in combat, just running. I approached the first tower, drawing the attention of the monsters to me, while Tonn was planting the bomb. I kept circling around whilst the monsters followed. Once the first demolition happened, I moved towards the second tower - same tactic. Then, I swam towards the third and Tonn followed. Bear in mind that during all these tower rushes, I killed nothing. After all, once the third tower is destroyed, a new sub-quest will ask you to eliminate the undead monsters at the beach (i.e. the beach surrounding the third tower). Once done, you can talk to Tony (you are asked to, anyway) and decide what you want to do. Still baffled by the developers on this one though. So many comments reporting this, but somehow they are unable to reproduce it. Well, ask the exact steps the players take - either they follow the quest's guidelines, indicating an inherent bug with the current system, or they try their own way, which appears to apply to many people - otherwise the bug wouldn't be so commonly reported -, thereby indicating a game-design/usability issue. Regardless of the case, fix it, so we all get over it.
