Add cards to deck

Hello, I added my 3 first decks to Anki today, every Deck about 17-18 cards by importing of csv. Everything is fine. I add fourth deck and want to add also about 18 cards to this deck with csv import, but I cannot add new cards for some reason to this fourth deck. deleted everything, tried with another csv files - the same. How to proceed?

can you provide some more information?

do you get any error message?
is there any difference between those csv files that you can import and the one that you can’t?
don’t exclude anything thinking that it might not be helpful.