I was previously able to upgrade my level 25 rank 3 adventurers to level 1 rank 4 but now when I try and upgrade them I get the message "This adventurer has reached the maximum rank." Is this a bug or has Plarium changed things without telling us? If this is an intended change then what is the point of winning level 25 adventurers in the coalition arena event? They may as well be level ones if all they are good for is upgrading guardians. I've patiently been upgrading my adventurers to level one of the next rank with the intention of  eventually getting four of them up to level one of rank 4 so that I can use them to upgrade a guardian to rank 5 and now that I've obtained and upgraded enough adventurers to grade 3 to do this I find that it won't let me upgrade any more of my rank 3 level 25 adventurers to rank 4. You can see from the screenshot that I have previously managed to upgrade rank 3 adventurers to rank 4 so why can't I do it now?