When I first learned about joseki, there’s a lot of move that I can’t comprehend, so I decided not to study joseki at all (except for some very common ones).
Now many of the moves that I didn’t understand in the past became clear, but still some remains a riddle.
Here I made a compilation of 4 questions that I still cannot answer. Maybe someone can provide his/her insight on these? It will be good study material I think. 
Very interesting questions! I posted some variations in the chat, they are my best guess about one of the questions. I couldn’t really answer the other ones, so I’ll wait for other people to chime in!
Oh, you’re right.
So I guess Black’s move in problem 3 really is a mistake then 
Some educated guesses. I hope that some stronger players will comment as well.
I left some variations about problem 1. I think that the aji left is not to be underestimated. Depending on the dircumstances, the white stone at Q14 is helping a white moyo while hampering a black one.
About problem nr 2: It depends on the rest of the board whether R14 was a mistake or not. Maybe R13 would have been better. Also the response Q15 might be mistake and a black answer at Q16 or at R12 might be more effective.
Is there a way to comment in the demo board at a move directly? I didn’t find a way to do it.
Hm I guess you can also fork the game if it gets too complicated.