Hello,
The design is pretty good to me, first of all. I wonder why the reviewer hard rejected this item 
. Because its a plugin, the code should be bulletproof, but I can’t tell you this without looking into it.
You are a plugin developer, make sure that your code comply with current standards + WP Standards. Maybe this is the problem.
P.S: My suggestion for you is to double check the code and make sure that it’s ok. The you should explain this into a future submission.
Good Luck 