It'll take some good hands-on troubleshooting to see what's going on when the problem occurs. Could be electrical, could even be software.
Use this link to find some shops near you that can help with your concern:
www.repairpal.com/repair-shops
RepairPal Certified shops can diagnose and repair your 2016 Mercedes-Benz SL550. They provide transparent pricing with a minimum 12-month or 12,000-mile warranty on repairs and services.