Braces removed 4 years ago and have permanent retainers. Started noticing a gap, do I need braces again? (photo)

I am male(24) had braces put on about 4 years ago but I noticed a small gap in my front teeth even though I have a permenent retainer. Is is worth getting braces again or should I go a different route? Also how did a gap appear if I have a permenant retainer