I'm not 100% sure why, but when I random elements the game has started giving me pure essences although I don't have any level 3 solo-element towers created.
I am aware that the game would check if you have any level three solo element towers to see if you want a pure essence or not, but now its doing it all the time. I think its counting all level 3 towers, regardless of how many elements they're comprised of, to check for pure essence granting.
Whatever the reason is, it makes playing random elements very trying.
edit: NM! Turns out that randoming Pure Essences is a feature, not a bug!