A couple of hours ago, I was using Iso to level up my Prof. X. After I was done, it showed I only needed 60,000 or so left. Now, it shows I need 98,000. No new covers were added.
What’s that all aboot?
It is not correct sometime, even when you have all 13 tokens.
It isn’t tell you the cost to max, it tells you the cost to level as high as you can with your current ISO + a $99 Mother Lode.
the button doesn’t necessary display the total iso cost to max if you don’t have enough iso to max the character. (see petergibbons’ post).
so the difference is likely that your iso stockpile changed TC.
Which always amuses and depresses me in equal parts. Hey MPQ Player! You can take that massive pile of ISO you have, spend $100 of your hard earned money to make your stash even bigger then dump it All into this 4* - AND STILL BE 40 LEVELS SHY OF MAXIMUM!!! What a great deal! 
This happens all the time I am doing my final push on 4hor initially called for 70K jumped to 90k the next morning after putting 16k in. Carnage who I just finished covering has no ISO in him and they claim it will take 80K to max, it seems to correct as you add iso. It is very frustrating though, it is a pain in the ass not know how much iso you need to finish.
Interesting. Never noticed this.
I noticed that it showed me an apparently arbitrary level to bring the character to, and I noticed that if I quit that character screen and came back it would update, but I never knew how it was derived. That’s kind of amusing, thanks!
the only one that has changed is devil dinosaur, it used to be cheaper to level him to max but now cost 70k more since championing.
It costs 366107 iso to level a 4* from 70 to 270.