As an occasional seller you are much more reliant on your Detailed Seller Ratings than those of us with steady sales.
I suspect your drop is because of that unhappy customer who left you a neutral, and trashed you on all your Ratings. And it is likely that others left positive feedback but did the same to Ratings. There are two 'false positives' in the past six months.
The neutral rolls off after 12 months, and I believe the Ratings do too. That will help.
I also looked at your lone listing, but the only possible problem I see there is your 5 day shipping window. There has been some spirited discussion about this and how it impacts TRS. You might want to check out the Seller Board for opinions.
You csn appeal your restrictions about every 30 days, by using Help and Contact at the bottom of this page. When you ask for a phone call you get a PIN to help you make contact.