My new LG G5 is now a brick, so I'm back to my slightly-cracked G4.
Yesterday, the phone got hot, stopped responding to inputs, and rebooted itself twice in three hours. That's usually the sign of a runaway app. So upon turning it back on, I manually rebooted it to clear running apps (it auto-loads apps that were running when it resets), and all seemed fine.
Then sometime while I walked home from Wrigley it shut itself off completely and has not yet woken up.
Fortunately T-Mobile was able to move my SIM back to my old phone. Unfortunately the photos I took at Wrigley were on an encrypted SD card which is now unreadable because the decryption keys are hardware-based. (The whole point of the encryption scheme is to prevent an attacker from moving the data to a new phone.)
T-Mobile says I should have a replacement G5 by Monday.