Freeform can’t create a link to share a board

One or two years ago I created a board for an exam. Now I want to send it to a friend of mine but when I click on any sharing option, a pop-up appears and it says that it was not possible to create a link for the board and to try again later. Could the problem be the size of the board? It’s very big. In fact, when I try to share smaller board it immediately lets me. Is there a size limit?