Update: Well dang. Seems the cache-wiping didn't have a lasting effect. The phone would be fine one day, wonky the next. I ended up returning the phone. Many thanks for trying to help.
Many thanks to UJ95x and belodian for the help. I followed belodian's link and was able to clear the cache and reboot.
Now we wait...will report back in a day or two with results!
Thanks, UJ95x. Booting into recovery mode and wiping caches sounds like a plan. Now, if only I knew how to do that! Yep, I'm one of those hopeless newbies. Will endeavor to figure it out.