Bali ash cloud
When Mt Rinjani on the island of Lombok erupted multiple times in 2016, it caused chaos for New Zealand travellers who had booked flights to and from Bali. The resulting ash cloud caused cancellations and disruptions to scores of flights in and out of Bali, leaving thousands of travellers with significant out-of-pocket expenses.
While those people who had taken out travel insurance before the first eruption were generally covered for those expenses, travellers who took out a policy after the ash cloud formed were not eligible for any benefits.