Until it is fixed, you should be able to use the following rules.
@treacle
Add the rule below in Main options > Fonts & Custom > Custom CSS Rule box for now
.atw-show-posts .atw-content-3-col:nth-of-type(3n+1) {clear:both;}
@on4ya Add the rule below to the same location But you will need to try 2n+1 or 2n as there is something strange on your page
#content .content-2-col:nth-of-type(2n) {clear:both;}
@weaver, there is something I don’t understand on on4ya’s page, the second rule for the 2 columns should be using nth-of-type(2n+1) , but for some reason, when I test 2n is what works on his page, I have no idea what is going on.
If I do a test page on my test site, the rule that works is the one using 2n+1 as it should
EDIT-1: Testing some more, it appears that if the navigation is present 2n is what works, but if the navigation is not present, 2n+1 is what works.
It is like the navigation is counted as one element although it does not carry the content-2-col class. I must be missing something about the logic of that CSS, will keep digging
EDIT-2: I just realized that nth of type does not care about the class… It is only caring about the HTML tag so in that case divs, which explains why if the Navigation is there, you need to use 2n. Because the navigation counts as the first element type.