Increasing tempremental G3 - rebooting more frequent

Hey,

I have a D855 G3. About a week ago it started to reboot sometimes whilst using Snapchat. It was infrequent and didn't really follow a pattern. It mostly happened with Snapchat but some days would be fine others not. It worried me as I've had a G3 replaced due to bootlooping in the past. Anyhow, this increased in frequency a few days ago up until yesterday where even a whiff of Snapchat would make it reboot and it rebooted a few times in Maps. It did bootloop a couple of times on the trot launching the lock screen (i.e. getting off the LG screen) but after a few seconds initiating another boot. I had to take the battery out, fully charge it, and then when I restarted it the next time I was able to uninstall Snapchat and I've avoided using Maps since.

Anyway, today it's been bad again and I'm worried it's going to slip into an infinite bootloot. It's fine with FB, texting, Instagram, Whatsapp. I upgraded Android today in hope of it fixing the problem, going from 5.1 to 6.0. No change. I tried installing Snapchat afterwards and it rebooted twice before being stable with no trace of Snpachat (despite it having just finished installing prior to rebooting). I tried installing another app, name has escaped me, but that caused a reboot and failed to materialise.

I just tried installing Google Clock and that worked fine. Er, I'm stumped really. I've taken my SD card out, stripped it of most of its apps. What could be the problem? It's all well that it works fine doing the basics but it's no fun not being able to install apps without fear of rebooting and not being able to use Snapchat is a bit rubbish (I'm sure it'd be a boon for some).

I really don't want it to bootloop, being without a phone at the moment would be very challenging. My contract is at an end soon so I can get another phone soon but I'd rather this being in working condition to give me time to decide/get more from resale.

TL:DR - LG G3 starting to reboot, sometimes bootlooping. In particular noticed with Snapchat but also when installing other apps so I'm avoiding that now. What could be wrong?