I wondered about this a few years ago when my home airport opened its new international terminal. The new security machinery means my stuff can make it through the xray long before I get through, leaving my phone, laptop, etc. exposed to anyone. I haven't heard of any local theft stories yet, but a coworker that I was travelling with a couple of years ago arrived in New York before he realized he'd left his laptop behind because he'd been separated from it for a few minutes, and it had been set aside. Luckily he got it back on our arrival home a couple of days later.
https://www.thrillist.com/news/nation/tsa-security-checkpoint-stolen-shoe-airport