It sounds like it could be a glitch with X Browser. You could send feedback to the developer from within the app's settings.
I'd also be a little cautious about saving sensitive information to that browser, unless you trust the developer completely.
When you say it "reset," do you mean it simply rebooted (like a power off/power on cycle? Or did it actually do a full factory reset, meaning you had to set the phone back up as if it were brand new?
Did this battery behavior suddenly start in the past month? If so, then it may be a known battery drain but that cropped up with the March or April update. I believe Google is aware of it and will hopefully fix it in the May update.
Welcome to Android Central! Also, when the phone is connected to the PC via USB cable, swipe down from the top of the phone screen to see your notification panel, and look for a USB notification. Tap that, and make sure it's set to "File Transfer."
Welcome to Android Central! For phones intended for the Chinese market, this is often impossible, unless you root the phone (and even then, it may not be possible). Whether that phone can be rooted is unclear -- you may want to check the forums at XDA-Developers.com, which is a better resource...
Are the missing messages from the iPhone user? Apple's implementation of RCS has been notoriously sketchy (which surprises no one, since Apple has dragged its feet forever about RCS compatibility).
I moved this from the Volunteer Hub to the Note8 forum, for more appropriate traffic.
Does this happen only when you're on certain apps, or does that even happen when you're just on the homescreen?