Are your frogs powered? Probably not. This creates a dead spot, and, if your wheels (and the rails adjacent to the frog) are not really clean, you're looking at stalling locomotives at some point.
On my layout, I powered the frogs, because there's not much more annoying than watching headlights flicker when a train is running. I'm using Hex Frog Juicers, which are, unfortunately, not inexpensive, but they work great. The frogs are all now powered, and I don't even have to worry about polarity. There's other options out there to power your frogs, too, e.g., Tortoise switch motors can be used to power frogs
Hope this helps,
DFF