I'd like to encourage you to have your students do a couple of things when they submit solutions, if you'd like to increase the chances that they will get mentored and selected for highlighting.
1. Check the box for "Free Mentoring" (or whichever form of paid mentoring that's appropriate). 2. Check the answer after clicking on Submit. 3. Follow the suggestions in the answer check for help with revising or for suggestions about comments which help them reflect on their work.
In a perfect world we would have time to mentor all submissions, but given limited resources, all these things help flag a student who is more likely to benefit from mentoring, and more likely to have a solution worth paying close attention to.