Short answer: Something on my network is causing the crashes.
I had an extra router, so I put it between my network and the TV.
Netflix no longer crashes, and other apps no longer give me the dreaded, "This app will now restart to free up more memory" error.
Longer answer: Netflix would regularly crash out to Live TV after 20-40 minutes of play. I've been on LG support with this for months. They've replaced the main board twice, and took it off-site where the problem could not be replicated.
I reset the TV and connected it to my smart phone data plan (luckily just upgraded to 10 GB). No crashes. Put the TV back on my network, crashed after half an hour.
I took the network cable out of the TV and plugged it into a spare WiFi router. This creates a small network of only one device (the TV). I no longer get crashes.
Unfortunately, this kills local network features like DLNA/Plex streaming and wireless display mirroring, but all Internet apps like Netflix and YouTube work flawlessly.
I plan to narrow down which device(s) on my network is the cause of the crashes, but after 10 months of fighting this I'm just going to enjoy some 4K streaming for a while. If I learn anything new, I'll post it here.