Yeah this came up last night where there was a tie and we interpreted the Conflicts section to mean that in the case of a tie, you are allowed to resolve ties in the most favorable manner for the investigators. Last night there was a situation where it benefited the investigators to be tied, so we ruled both got it. In the case of a tie where it would hurt the investigators, then only one investigator would be affected by this. I couldn't find anything else in resolving ties except the Conflict section.
You can't resolve a tie as it being a tie. That doesn't make any sense. If the instruction says something good happens to the investigator with the highest Strength, or whatever, then you choose one of the Investigators with the highest Strength.
You can't choose to happen to all of them, as the events are designed to happen to one player, good or bad.