You have had bad luck, that cost falls within the range of bad luck that you can have, an object needs approximately between 1 and 35 attempts per level using the tools to go up a level or go up to level 16. If you use the yellow button there is no limit of unsuccessful attempts, each attempt has an X% to go up and directly you can have very bad luck or good luck

I have to say that, I feel it too, but still need to check further, because I only have 2 artifacts upgrade events to compare to.

The first time around it took me 15 mil silver to get ALL of the prize on the artifact upgrade event, but the second one with the same amount of silver it only get me 2/3 of the total points to get the full reward

But again this is just a conjecture, and there's a probability that there's a different use of the upgrade (more +12 upgrade on more heroes vs +16 on fewer heroes)

You should start counting the number of fails each level, in the past the number should never pass 32. If it passes 32, means Plarium already increase the fail limit.