All we know (if I've understood correctly) is that there were problems in multiplayer concerning players being able to see eachother through walls by way of the mouseover/aim/cutaway feature.  Their remedy was to remove that feature and leave us with only the passive proximity based building cutaway.  One of my speculations was that maybe the problem has to do with the way the game handles visibility through openings but I really don't know.  I believe they did substantial reworking of the viewcone in B42 so it's rational to suspect there are some fundamental problems causing all of these loosely related visibility issues.

But how would the cutout system be affected if they were doing other things? Were they trying to enhance the system or something but it broke?

As the title suggests. When wearing gas masks, respirators or welding masks (something that's not textile overall) to muffle the voice of our characters.

There are indications of some deeper issues with the way the viewcone reconciles walls, doors and windows, hence why they made the unpopular decision to limit building cutaway.  The devs have been semi-open about the problems.. enough to address the complaints and to confirm that they are aware of the issues but we can basically only wait and see what, if anything, becomes of it.   As it is, I can't say for certain if what you're noticing is related to changes they've made in attempts to mitigate some of the "xray vision" problems but it's a plausible hypothesis.  We can only speculate.

Version: 42.19 Mode: Single player Mods: none Reproduction steps:  1. Spawn in at cords 2. Walk through counter by bottom of stairs 3. ... Coordinates are X:10751 Y:10593 Z:0