Finding checkmate sequence / Successful attack completion Among my weaknesses (which I am aware of), the most irritating and the most important for me, at this point, is "checkmate blindness", whether because of time pressure or because of any other reason.

Most of the time I am able to develop a pretty tough attack that forces my opponent to defend and not letting him to seize the initiative.

The problem is that I can't see, too often (!), a forced checkmate sequence and sometimes even mate in 1. Despite the fact that I am familiar with all checkmate patterns and easily checkmating a lonely king with knight+bishop etc.

My question is what is a good way to improve those checkmating skills when the board is not empty and the checkmate is not obvious?
Solving checkmate puzzles doesn't help me too much because I know that the checkmate is unavoidable and I am able to find it. 

For example, this is a game I played yesterday (white). Eventually, I won this game but I did not find the checkmate sequence 5 times!
https://en.lichess.org/B6FRwado
It's one thing to be aware of the checkmating patterns, but it's another to have them fully cemented in your mind.  The key here would for you to develop pattern recognition, which happens when you practice these checkmating tactics so much you can almost instantly see them in a real game.

I would suggest just solving countless checkmating tactics day after day.  Do problems that have lots of pieces on the board - the checkmating patterns against a lone King, for example, won't help you much in a complex middlegame.  Probably the best idea would be to buy a tactics book that either focuses on checkmate tactics or at least has an entire chapter dedicated to it.  The other option would be to do online chess tactics, although I don't know of a site that allows you to pick which kind of tactics you want to do.

One chess book you could check out is: "1001 Deadly Checkmates by John Nunn".  It's a fairly well recommended book.