Sun Mar 04, 2018 11:07 am
I checked the event, there is nothing in it that would make this happen as you describe; the chance is 15% (so not high) and the worst that could happen is 10% losses and -25% cohesion...not exactly what you describe, so without a save I can't figure it out.
There is a Great Plague event later in the GNW that is very very severe, may be it is this one. But I can't guess (no save) because we don't know what you are playing here.