no unbreaking 3 in librarian villager book pool

So I made a server for me and my friends and we have gotten to the near late game stage. we have had villagers for a while but until now had not grinded librarians much. in abt 13h of trying for unbreaking 3 we have not gotten any unbreaking's at all. in that time we have gotten mending 7ish times. it may be just be bad luck, but this does not feel right  

 

Update. got unbreaking 1 on a LVL 3 trade on a random villager after 4 more hours of trying