I was making a very large junction, and I found a bug: the flashing signal is working correctly (can be seen with the chain signal before the normal signal: it is green, but it would be red if the normal signal was not working)
gif
Gif of the flashing signal
ezgif.com-crop.gif (5.58 MiB) Viewed 1249 times
So the problem here is that the signal is flashing even though it works.
This also happens if you replace it with a chain signal, or remove it and then place a (chain) signal back.