Something that the old Source mods used to have to deal with was 'zoned' sounds. I remember that the map designers for some of the mods I played had to be especially careful that they did this part right because otherwise someone stood in the next area through a doorway or whatever might as well have been in the vacuum of space, because you couldn't hear their gun firing, but you could hear the ricochets and bullets zinging from the wall behind you in your area.
I had it explained to me in laymans terms (and this was a decade ago so sorry if this is inaccurate) but the idea was that there were only so many sounds able to be played at once before the engine would start to do some unexpected things, so the way teams got around it was to compartmentalise maps so that only so many sounds could be heard from each section. If these areas weren't cross-referenced properly you'd end up with the unusual situation where someone could be right next to you firing/walking but because they were in a separate zone, you couldn't hear them.
I was told that Respawn are using a modified version of the Source engine : and the sound thing might be some limitation they've not explored fully if this sound-zoning mechanic is still part of it. Certainly the map for Apex is larger than any of the mod maps or HL2 level maps that I remember by a large margin. If it's all 1 big zone then they may be experiencing some of the unusual sound crap from the old days.
The reason this sticks in my mind is you used to be able to totally crap-out Apex's sound by launching a Pathfinder ultimate at an Octane jump pad, or by a deathbox landing on an Octane jump pad and settling there. You'd get the rapid repetition of the jumppad noise which wouldn't just drown out other sounds with volume - it would actually stop ALL other sounds from even playing. You could fire your gun and not hear anything, you could throw grenades and the sound of the explosion wouldn't even play.
[edit] - So to bring this back to the real world from the Hypothetical : @Tperodactyl 's video might be the result of multiple gun battles going on all around the map, and the sound effect limit being hit, even though he is too far away from most of the fights to be hearing them. If the engine is producing them all and working to ITS limit rather than the limit of what his client should be producing as actual sounds for where he is stood - it would explain the missing footsteps. I'll use arbitrary values because this is all guesswork but if the engine is willing to play a maximum of 1500 sounds at once in an area, and it sees the entire map as 1 area, then even if he isn't close enough to actually HEAR the sounds through his client: every Flyer scream, footstep, ambient sound, grenade explosion, reload sound, grenade 'ready' sound when someone pulls out a grenade counts towards that total. Once it's reached, the weird stuff starts to happen.
What's weird is that we're not seeing it with people running up to us and their guns not making any noise, or grenades not making any noise. There's something specific to footsteps. It's as if the footstep sounds are prioritised last to avoid the situation of someone lighting you up with a Spitfire but the gun not making any noise.
The base engine they've modified is from a game released in 2004, so archaic problems when we get to the more esoteric bugs etc isn't that unusual.
