Comment by pixl97

>hide for years in application code

Yea, it's pretty common. We had a customer years ago that was having a rare and random application crash under load. Never could figure out where it was from. Quite some time later a batch load interface was added to the app and with the rate things were input with it the crash could be triggered reliably.

It's something else that's added/changed in the application that eventually makes the bug stand out.