Continuity mistake: Just before Steve Hadley is killed by the Merman, his tie is wrapped around his neck. When the Merman attacks him, his tie is worn properly. (01:19:40)
Continuity mistake: Before Dana and Marty enter the control room and release all the monsters into the control centre, there is a thermos flask and a torch sitting next to each other on the control room's desk. But once they enter the control room, the position of the thermos flask and torch have changed without anyone touching them.
Continuity mistake: When Curt is reversing the van from the crumbling tunnel, he's shown sticking his head out the window, then looking forward and again with his head out the window in the same shot.
Plot hole: Marty Mikalski discovers a micro-camera in the cabin and is immediately grabbed by the cursed zombie Judah Bruckner, who drags Marty through the window and plants a machete in Marty's back. In that shot, the machete is obviously buried in Marty's back, which should have broken ribs both back and front, severed spinal nerves, penetrated arteries (as well as the right lung), and protruded from his chest. Marty was dead on arrival in that one stroke. Yet Marty emerges at the end of the film as the hero, with no gushing blood from his back or chest or mouth, and no explanation of how he miraculously removed the machete from his back.
Plot hole: When Dana realizes that the puppeteers made them choose their own deaths (while standing in front of Fornicus in the elevator) she does so by watching the puzzle ball he holds. But she never saw the puzzle ball back in the cellar. Only Curt handled it briefly and is shown approaching her without it when she starts reading the diary.
Continuity mistake: When Lin is talking to Truman and says that they're all just letting off steam, the position of her hair on her left shoulder moves between shots.
Continuity mistake: This is just after Curt has jumped into the lake. The green towel around Marty's neck disappears and reappears. (00:22:00)
Continuity mistake: Aren't the survivors trying to escape by traveling through the tunnel in the same direction they took to arrive?
Other mistake: When Curt crashes into the force field when he is trying to jump the gap on his dirt bike, his point of impact is ridiculously high up. (00:59:40)
Answer: It's stated that the tunnel should have blown hours ago, so the initial failure is most likely human error, that the order to blow the tunnel simply didn't get through to the demolition team on schedule. The subsequent problem blowing it up is referred to as being related to "a glitch up top", later stated as a "power re-route upstairs". While not stated outright, the only plausible explanation is that this was, as you rightly stated, due to Marty messing around with the equipment that he found in the hatch.
Tailkinker ★