Add Pages -> Collections won't show templates

Hay lovely people of Squarespace Forum, 

I have a peculiar problem it seems. 

I'm building two new sites and started my trial in late august. I was able to work on it a bit, adding pages; blanks, contact, blog pages, etc. All was accessible. 
When I came back a small week later I wasn't able to add pages like Collections anymore, only blank pages. The window for (example Blog) pages opens, but the templates don't show, and therefor I can't click on any, and not add such a page. 
I checked with my other sites (both in trial mode and published) and none of them are able to add collection pages because the templates don't show. BUT on any other computer it DOES work. 

I have tried everything I can come up with; deleting cookies and cache, checking extensions, opening squarespace in a private window,... nothing works. It is becoming quite the annoying mystery. Anyone any tips?

This is how pages -> + -> Add Blog ->                                looks like:

Hi. Have you solved it yet?

No, I haven't been able to solve it! 

Hi! I haven't experienced that same issue before, but in addition to what you've already tried, I would maybe try logging out and then back in to your Squarespace account (and make sure you don't have any pop-up blockers or VPNs on just in case that's somehow affecting it, shouldn't be, but always worth a shot).