Couldn't buy Rengar (Champion) to upgrade

Weird bug:

I needed 1 Rengar to get my 3rd level Rengar upgrade. Rengar appears after a reroll in the last slot (far right). Click on it = can't buy. Click repeatedly, no can do.

Had a free slot. Had a Rengar in play Had one at level 2 in my first slot and 2 other next to it at level 1.

Had the money. Wasn't in a fight. Still in the countdown before fight.

Really weird.