ICN, in my experience going back many years, is notorious for its transfer security, which is often a debacle.

1. there is no premium line for business/first or elite frequent flyers. In the summer, there is barely any ventilation or air conditioning in the transfer room
2. their screeners find the smallest, most minute, irrelevant items in carry-on bags and then lose their minds over such items - specifically for years they have gone absolutely nuts over my small plastic bags of coins. Last July they couldn't accept the existence of keys in my bag - they took the keys out and put them through the x-ray multiple times. It took all of my energy not to slap them upside the head. The same screener took out my bottle of medication, argued with me over prescription rules, then when he finally said "it's OK" dropped it on the floor trying to put it back in the bag, so I discarded it anyway. That deserved another slap upside the head.
3. last week, like a miracle, my bag still with some coins, keys and stuffed with charging cables sailed through without a glance - but my spouses bag was stopped. What we saw on the screen was a coil of cables attached to a structure which honestly looked like a crude bomb - but no - what the x-ray tech saw was their teeny-tiny nail clipper which was buried in the cosmetics kit, which was then dumped out onto the tray, the nail clipper held into the air for visual examination, being an obvious instrument of deadly violence - before being cleared. We ended up with that screener because the one in the adjacent line was spending 5 minutes with each passenger staring at their boarding pass, itinerary or passport like he had never seen one before and thought it might be a winning lotto ticket.

The room filled up behind us, almost spilling out into the hallway, and they still refused to open more than two lanes.