i use a trigger on the default branch. It was temporarily disabled. After re-enabling it, the trigger did not fire.
In general the build log does report the conditions that successfully activate a trigger. However there is no log information, when a trigger does not fulfill conditions. I did not find any information in the event log. Imo activating debug logging for such an issue is not an option. Especially since the situation, when the trigger did not fire, is over any.