I think you should check what has happened on server side, because the request durations are very high. Dropped iteration happens when k6 has to run an iteration, but there are no free VU, because every VU is allready working on a previous iteration. If a http request lasts for 58 seconds, that VU is busy for at least 58 seconds. Interrupted iteration may happen, because it is not finished after the test duration (+gracefulStop period, which is 30s by default)