OK! I went back and thought about every change I’ve made before building the lighting, and here’s what I found out.
I set the shaft of the torch to not use lighting channel 0 and use lighting channel 1 instead (to avoid weird lighting from the stationary point light on top of the torch). And then I enabled lighting channel 1 on the stationary point light at the lantern, so it could still affect the torch’s shaft. And for some reason that bugged out spotlights that had light function to simulate water ripple reflections. After I enabled light channel 1 on those spot lights as well, the bug went away.