I was just in the lounge two weeks ago 12/20 before my flight to BKK (early evening like 5-6 PM). I am a regular Morning Calm member. I visited the Prestige Lounge East (it's weird because when you walk in the airport - it's on your FAR LEFT which feels like west end). There was a sign outside stating that due to overcrowding, Morning Calm and other partner members may not be able to enter. They didn't stop me from getting in though. The "West Lounge" (which feels more in the center) was so busy there was a line to get in (but no overcrowding denial sign).
That being said, if it's a shower you want - the KE lounges only have 1 shower so I'm told. There are FREE showers for transit passengers in the 4th floor Rest & Relax area airside of both terminals in ICN. I've used them and they are absolutely lounge quality. Free towels and toiletries, of course. So don't pass up ICN because of a KE lounge shower when you can get one easily on your own.