The recent CS:GO update brought a variety of changes to our favourite FPS title - fixes to the CZ-75, buffs to the Tec-9, a change in casual map rotation, as well as the introduction of the MP5 to competitive match-making. Additionally, prices of both the AUG and SG 553 were reduced by $250, making both rifles a lot more usable.
A large proponent of this was Team Liquid's rifler, Jonathan "EliGE" Jablonowski, who said that not only will the SG 553 see more air time in professional matches, but will also become the weapon of choice for a lot of pros:
I actually see most pros swapping to only using the krieg as soon as everyone gets used to the recoil within the month. It’s just way better— Jonathan Jablonowski (@EliGE) October 9, 2018
A short while after the patch, Jablonowski booted up his stream where he was practicing the use of the scoped rifle. A user watching his stream tried to recreate a wall-bang on Cache, only to discover that the rifle was unable to penetrate a sheet of metal covering Z:
This was later confirmed to be the case through recreation, and the issue was escalated to well-known map designer, FMPONE, the creator of maps such as Santorini and Sub-Zero, as well as the map in question, Cache. The issue proved to be much more involved than a simple mis-map, as per an explanation from Reddit user /u/SlothSquadron:
In addition to the "Penetration Power" stat (buymenu lists this as 200 for both AK and SG553), damage also plays a role in how well a gun can wallbang. The AK has a base damage of 36 while the SG553 has a base damage of 30. While the SG's armor pen is significantly higher than the AK's (100% vs 77.5%), armor pen plays no role in wallbanging.
The AUG also suffers from the same issue, (28 base damage vs the M4's 33) so its wallbanging is also worse than the M4.
Also wallbanging does take into account damage falloff with distance. You might find you're able to wallbang a surface up close but if you try and do it at long distance the falloff will make you unable to wallbang.
The issue seems to be that a multitude of gun statistics contribute to a weapon's penetration power, including base damage of a weapon. As explained, the SG 553 has a lower base damage than that of an AK-47 or Deagle. As per the demonstration by Savjy above, this leads to the Krieg's inability to penetrate the metal sheet, while both previous weapons do so with ease.
In the Reddit thread, FMPONE expressed that it might be a good idea for Valve to rework the buy menu and weapon statistics interface to better inform users of the values for each gun that they use.