PS2 Smoke units shut off, then go back on???

I am a member of a train club with a modualar layout. This past weekend, i was running a lashup of 4 MTH PS2 AC4400s pulling a little over 50 coalporter hoppers. All 4 engines have 3 volt boards. When the engines entered the tunnel on on of the curves, the smoke units shut off, then seemed to come back on quickly there after, almost immediately after. Sometimes all 4 engines lost the smoke, sometimes it seemed only 2 or 3 out of the 4 lost it. It is a possibility all 4 lost it every time, and just a few were quicker than others to come back on. We put on an MTH UP 4-12-2 steamer, and ran it at the same speed about 12' ahead of the AC4400s, and it never lost the smoke once. I'm confused here. I thought perhaps the engines were losing signal in the tunnel. But I was under the impression when an engine loses signal, it just keeps doing what it is currently doing until it recieves a signal to do something different. I've ran many differnt engine combos on this layout over the past 2 years, and 3 times at this particular venue, and this is the 1st time I've encountered this. Any ideas why? Or has anyone else experiences this? I'm stumped on this one! Here is a little video of them running which i took with my iphone...