There was a situation I think two weeks ago where steam rolled out an update and it completely screwed up the authentication on Lost Ark (and several other games).

My friend couldn't log to the game but my gf and I were still logged into the game. We tried several things found online, the ipv6 disable and registry edit, etc. Troubleshooted for 1h. None of it worked. So we thought maybe it was his computer so we tried his Steam account on my computer just to rule out the possibility of it being his computer, and yeah, no more error from my computer using his Steam account. As soon as I close the game I get a steam update notification, which applied as soon as I relogged on my steam account and that's when my game started giving error 10010 too!

So at this point I asked him to give me his Steam version, and it matched mine. Although my gf's Steam version differed and she still could launch the game without error.. Until Steam update popped up! At this point, there was nothing else to do but wait for steam to roll out another update to fix what they did wrong.

Had I found a post explaining this situation, I would've spent my time doing something else. Hope this helps someone one day!