We would need a lot more info on this to work out what may be causing this.
The first thing to check is the type of signal you are using. For Trainz, there are two different forms of 'red' signal in the default signal aspects; the first is a standard 'stop' aspect which the AI should stop for (if given enough time to stop), the second is the 'permissive' aspect, this type of signal is a red signal that can be passed with caution (in reality you would generally stop, wait for a certain period of time, then continue; for the AI they treat it like a signal where it continues at half the speed limit).
The second is to check the speed limits approaching the signals and the distance between signals; if the speed is too high for the distance between signals then it may not have enough time after passing a caution signal to slow down and stop for the red signal; after passing an actual 'stop' signal the AI will stop and wait for a set time and then continue on with caution till the next signal.
However if you have a reproducible case of AI trains ignoring red signals, then please make sure you have submitted a bug report to our bug report form at https://n3vgames.typeform.com/to/xRdryu with an example session that shows the issue.
I have the issue with AI trains passing the red signals as well, usually its when they follow another AI train that stops at a signal but the cars behind the locomotive "sway" a little bit back and forth after the train comes to a stop, causing the signals behind the train to show red until there is another junction on the section of track the train is running on(I guess the signals detect the movement in the opposite direction, even though its minimal its still detected to the next junction).
This has been a bug since TRS19 physics and happens with all signals built in or not.
Another thing I noticed is that when you zoom out of a layout into map view, the clock in the right corner disappears but the underlay stays visible. Not sure if its a bug or intentional but I don't understand why the clock disappears while all the other interface items stay visible?