Half-Life 2 just got a small update, mostly to fix a long-running music bug. But hiding in the patch notes is an apology of sorts, a nod to that most tenacious of bunnyhopper: the Half-Life 2 speedrunner.
It seems the recent 20th anniversary update for the classic first-person shooter messed with some beginner speedrun strategies by introducing an invisible wall to a big sewer pipe.
Valve have now corrected that, removing the offending blocker and restoring order to the universe. Well, almost. "Removed collision from an underwater tube that speed runners enjoy," write the developers in the update post, with traditional Valve inscrutability.
They're talking about a large pipe in the sewers of the Route Kanal sequence, which you've got to flood with water to pass through (you can see said pipe in this playthrough).
It seems Valve always intended for this pipe to have a big "player clip" over it - an invisible wall you can see in the map editor image below.