i've found the way to somehow fix it temporarly - I have to add i.e. "-1" at the end of URL in every product, adding this traffic section of preferences does nothing. Ok, sure, I can add this to every product, but it's not the correct way to deal with this problem, I want to keep old URLs from old shop and not remember to add something to URL
I can see the pattern now- when URL is ended with letter it's not working, if it ends with number (when it is generated by presta or added by me) it works fine. What can be wrong?