Difficulties in getting phone to boot and/or into recovery mode.

Phone owner states the phone was operating perfectly normally. He went to Whole Foods and connected to its wifi. Almost immediately the phone rebooted, crashed, rebooted again, crashed, over and over again until the battery drained.

Plugging the phone into a charger for ~60 minutes does not seem to charge it; the battery indicator comes up as "0%" with a graphic to plug it into a charger. However, you can take the phone off the charger and turn it on and it does go through a sort-of boot process which indicates it actually is charging, despite its claim.

If I try to do a standard boot, the phone buzzes (to indicate it's turning on) and immediately shows "RECOVERY BOOTING..." in the upper-left corner. After a few seconds the screen turns blue with an Android logo and "INSTALLING SYSTEM UPDATE" underneath; literally one second later there's a "broken Android" symbol and "NO COMMAND" underneath.

If I try to do a Safe Mode boot, the same thing happens except when the "RECOVERY BOOTING..." part comes up, the "Samsung Galaxy S7 Edge" splash screen also comes up.

I'm able to go into Maintenance Boot Mode (POWER + VOLUME DOWN) but there's nothing useful there, unless I want to wipe the phone and for now I'd like to avoid that. I also can't seem to power down the phone via Maintenance Boot Mode. When I select it the phone freezes butnever actually shuts down -- until the battery drains enough, at least.

Attempting to go into Recovery Mode (POWER + HOME + VOLUME UP) is unsuccessful, giving the same results as a standard boot.

Ideas?