The video below shows exactly what happened but I'll explain up here for anyone who doesn't want to watch it. On my approach to Bochum station I passed a yellow light and acknowledged it with the PZB. However, the 1000Hz magnet never came alive. The 1000Hz magnet only activated once I passed the second signal, the red one. So in my opinion what happened is that the signals were just showing the wrong colours as the magnets worked where they were supposed to and it did not fail me when I passed the red signal.
Yep, unfortunately you will find a couple of these bugs around a lot of German DLCs. I find it very common that PZB is not always triggered when it actually should, especially on older DLCs, however, you will also find it on newer routes.
Now that I have watched the video 3 - 4 times I think the problem is not the PZB but the colour of the signals. I think the yellow should have been a green and the red should have been a yellow as when I passed over it not only did the 1000Hz activate but I did not fail the service wich means that the signal as far as the internals of the game is concerned was not red.
Indeed. It is well known that DTG failed to model the Ks signalling system correctly on HRR. The first one you passed should have have been green, the second one was yellow. Unfortunately, you triggered another bug when contacting the dispatcher: On German routes, contacting the dispatcher while having a not-red signal turns all not-red signals red (just visually - they‘re not treated as red signals). So you‘re second signal was yellow, but appeared red because you contacted the dispatcher. Tl;dr: DTG messed up the Ks signals - instead of green-yellow-red, they give you yellow-yellow-red as the signal progression to a stop.
DTGs implementation of the Ks signal system has some serious flaws, this being the most annoying of them, I hope they fix this soon!