4 prints, loose belt..?

Hi all,

So I'm a new owner of a Da Vinci 1.0a, done around 4 prints and I've noticed that sometimes the right-hand belt is dropping down and showing some slack. However, this is not constant and sometimes the belt seems to be just as taught as the others, anyone else come across this? So after noticing this and it not actually seeming to affect prints, now it has started slipping and producing some horrific results (obviously, see below).

I would appreciate any advice from someone who has knowledge/has experienced this before, is it merely a loose belt? Could something else be at fault - which would explain the belt not permanently showing slack.

Thanks in advance