I was driving the black train at the bottom. Right after this happened I got out and took the picture. There are four vertical rails, from left to right going up/down/up/down. So it's essentially two identical two-way lanes side by side, and the crossing here is what lets trains move between these two-ways. The white train coming from above had just left the nearby station so it was not going at full speed. The red train coming from the bottom was going at full speed, or very close to it.
I was not placing or removing rail, I was not driving either of the collided trains. The only thing I was doing that could have to do with this bug, was that I was driving through that same crossing in a separate manually controlled train, at low speed.
Attached is the save file right after the collision. I also have an autosave from before, but I couldn't get the collision to reproduce. This leads me to think that me driving past in a manual train has a LOT to do with this case, as it would be impossible to replicate that exact situation manually due to be driving at low speed instead of full speed (so the timing would always be barely off, allowing for a safe crossing). As usual I was playing a vanilla save without any enabled mods. I checked the logfile but all it did was autosave 2 minutes before, and a minute after the collision - no other logs inbetween there.
