iPhone Pro Max Shutdown

My iPhone Pro Max 11 shuts down daily where I have to do a forced reset. I've even reset and erased all contents, removed unused apps and closed down open app routinely during the day and it still shuts down. Even happens with 100% battery life. Opened a ticket with Apple Support who sent me to an authorized repair shop and they determined there is nothing wrong using an automated troubleshooting process with Apple. It's not exactly a great time to have phone issues. Any suggestions? Thanks