You package your game (not Shipping mode) to desktop.
launch game, play a little; there should be a Logs folder within “Saved” folder inside your packaged directory after you play the game. There should be logs recorded in there.
Btw, I just packaged one of my personal home projects, and pooling is working on the packaged game (4.19).
That error you see in your logs usually means that the Pool Component or its Owner has been deleted or is marked “Pending Kill” while Pooled Actors were still being pooled from that Component.
That shouldn’t happen, this is why I wrote that warning to show up there. It says something is wrong about the lifetime of your Pool Component (probably destroyed for some reason)