I have just installed LOKI in two PCs and I am having the same issue with both.
On App Center I can see the apps list; however when I choose any of them, click Install and I can see the progress bar, but nothing more happens.
Please note that after install I managed to install sucessfully with App Center a few tools; However I disabled the Guest account and since then I can't install anything. I tried to reboot several times and to enable again the Guest Account - however the problem persists.
Additional info: Default language is PT-pt, but this change was one of the firsts - after change language I managed to install a few tools.