Hi Noe,
Differences of a few milliseconds are to be expected: executing commands from the script takes time, and sometimes browsers experience light slowdowns, resulting in slight delays between a log command being executed and the creation/assignment of the Var element targeting the event.
The command shuffle regularly intersperse trials from two sets of trials, while randomize randomly reorders all the trials in a given set. You can always replace shuffle(randomize("..."), randomize("..."), ...) with the shorthand rshuffle("...", "...", ...). But since in your case you only have one set of trials (“experimento”) you can just use randomize like you tried at first
Try a hard refresh on your experiment’s page and you should see a new order (sometimes it takes several shots if you only have a couple trials in the set, because there only are so many possible permutations)
Jeremy