If your gig is losing rank there could be some factors to this but it's hard to know exactly. Fiverr is highly competitive and you need to keep evolving.
Here are some tips that help me:
Check your best competition that sells the same with a similar price. What are they offering?
Are you doing your best and are clients feeling they are getting good value for money?
It is possible that they are giving you good ratings but giving you private negative feedback (this sux). Make sure you get back to your clients, touching base, asking if there is anything else you can do for them. Be connected to them. Also give updates every few days on where you are at.
Always update your gigs. Never let your gigs go stagnant. Always think on improvements, can you offer something extra? Can you improve on your communication skills? How about the gig visually? Is there any room for improvement?
Best of luck.