I would wonder if r7800 isn't stable because it is the most popular modern router in this community.
First you should change the topic into sth. like: "Netgear R7800 randomly crashes". To get the attention of other R7800 users. I forgot that to mention before.
There are two threads in this forum where you could search if there is an stability issue on the WAN interface.
Second link is a community build by hnyman. You could try this build and see if the issue is solved there. There is a master and 19.07 build available.
You could provide/check the bootlog/syslog for any errors also. You could test with a fully reseted device (just plain internet configuration), to see if the crashes remain. In addition you could revert back to factory firmware to see if the router is stable then and possibly conclude to an OpenWrt related issue. For me (I may be wrong) it looks like an Wifi related issue. Is your internet connection stable if Wifi is disabled? If yes then you the error could be found in your configuration (uci show wireless).
Another possibility is a faulty cable (try to change). If that does not solve your problem it could be a hardware failure or maybe the modem in front is causing internet connection issues.