I tried to load a savegame and right after loading I saw that all of the rails signals, including chain signals gave the error state.
as if each individual signal is thinking he is all alone out there, and trains don't notice them anymore ( a lot of crashes in the first 30 seconds when looking at the right spot

the savefile was saved in 16.39
removing and replacing the signals helps, but only for the ones replaced, the old signals don't recognize the new ones, nor visa versa.
when saving the game and loading it again, also only the newly placed ones are working, and the old ones still the error state.
in this savegame only the signals on screen are replaced, all of the other signals in the world are from before 16.40