Expedition explosives sometimes get stuck before exploding

I just got an 8-mod Expedition encounter (with "Very Rare Unique" as reward) that I couldn't complete because the explosion didn't happen. I've put the explosives down, started the encounter, it fizzled out and the chain never started exploding

I think it's either because the wires got crossed at the beginning or because a bell might've spawned on top of the explosion area. Idk