Why is my recently new s5 constantly crashing and turned into a custom rom after a reboot?

[AC Question]

Got this phone three weeks ago. At first this phone crash randomly and a factory reset would fix it. But starting yesterday, it became a custom rom and the crashes were every minute or so. Today, it is in a constant boot loop and it crashes before the apps are optimized. I have tried wiping the cache partition to no avail.