Thanks a lot for the detailed feedback, I'm glad you enjoyed the game overall.
Except for SMGs which are unlimited just like knifes you actually get weapons along the way but the only way to notice you did find a weapon is a very light sound which could mean anything and the text saying you got one under the 'change weapon' command until you press this button.
The 4th level contains tons of (intentional) invisible walls, I don't think it's actually bugged but lack of feedback explaining what's going on might basically feel the same in practice.
There's one more level after this one.
I'm going to watch your playthrough for sure.