I'm not quite sure if this issue have been fixed in new versions of the plugin, but after some months trying to fix the sorting by time, price I found the solution here: https://forums.osclass.org/general-help/sorting-not-working-regardless-of-friendly-url's-beuing-enabled/
Efectively by disabling the the option "Improve search in way that premium listings are shown first" my sorting issues got solved... By the way I'm using a modified version of Bender theme.

@tabuausada
Thanks, will check that.