343 Industries says that the devs who would fix it are working on other things.
Halo Infinite multiplayer

An issue that has plagued Halo Infinite's multiplayer mode may not get fixed any time soon, or possibly at all. At seemingly random times, there will be some synchronization issues in multiplayer that lead to situations where melee attacks just flat out don't register. The client and server each think that the players are in different positions than what the player sees on their screen.

On Monday, a Reddit post (via VGC) was made that yet again complained about the melee collision being "still incredibly broken." The post showed a video of the issue in question. It was replied to by senior sandbox designer at 343 Industries, Brian Berryhill. Using the Reddit name of "343_Taxi," Berryhill flatly said that "the devs that would work on these fixes have been allocated to other Infinite work."

Berryhill's full statement can be read below.

Just wanted to comment that we appreciate these types of compilations. Videos like this always get pulled into bug/task threads for UCN (networking) improvements.

I don't know if twitter/reddit is the best place to go into all the details about why there's been a lack of UCN improvement, there's a lot of factors, so I'll keep it brief. The TLDR of it is the devs that would work on these fixes have been allocated to other Infinite work. Their work has had some knock on benefit to our UCN solution, especially around movers (players, vehicles, etc.) on object devices (elevators, pistons, bridges etc.), but not around the melee and "around the wall" shots. These devs are coming home to Sandbox soon (hopefully)

The Community and Competitive Insights teams have done an amazing job at letting us know how frustrating these kind of situations are. It is high on our priority of fixes.
While it wasn't stated what the networking-focused developers were working on, it's probably a safe assumption that they are working on getting Infinite's campaign co-op up to snuff before release.

This isn't the first time that Berryhill replied to a complaint about this desync bug. About six months back, Berryhill replied to a similar complaint. At the time, he said "If we can repro the issue with our latest internal builds, we’ll get a bug triaged for it and start doing a deeper dive on it."