Valve added an invisible wall to this sewer pipe in Half-Life 2 in their anniversary update - but it only annoyed speedrunners

Barely a bug IMO - Valve wanted an invisible wall to block players from being able to skip a small environmental puzzle, but invisible walls are a lazy solution. If the player can find an alternate route to climb up into the pipe, more power to them I say.

That's not really the case, though. Blocking that pipe off doesn't fix any bug, it's just a design choice to tell inventive players that they must solve the puzzle before continuing. Removing that and allowing players to progress without having solved the puzzle in its intended way is just a different design choice. Both are equally valid, in my opinion.

There actually have been quite a lot of bugfixes in the 20th anniversary update, which have an impact on current speedrunning tactics, as can be seen here within the section 20th Anniversary update of Half-Life 2. In the end, it's pretty meaningless anyway, as most speedrunning of Half-Life 2 is done with a pretty ancient version of the game.