Atm I'm running a self compiled OpenWRT on a 841nd v5 (with a couple of things removed) and this is the last commit that it's included in my build: https://git.openwrt.org/?p=openwrt/openwrt.git;a=commit;h=cc78f934a9466a0ef404bb169cc42680c7501d02
(last commit just before " kernel: bump 4.9 to 4.9.214") without having issues (Luci is happy working and I have over 2 week uptime).
I mostly upgrade between my own builds ~ 1 time each month and I usualy keep the settings (because I'm too lazy to remake them) and I don't remember an issue with Luci crashing.
I did had an issue last year with my builds restarting the router every 2 min (it was stable only if I was clearing all the settings, the smallest config change was triggering the reboot every 2 min) but it looks like Ubuntu messed up something in their kernel, reverting to an older kernel on the build machine generated builds that were working without problems. (dmesg on the build machine was showing a crash related to igpu, something that well was happening ~2015 based on my google searches...). I changed to Manjaro due to this particular issue with Ubuntu (no issues with Manjaro and latest stable kernel, no crash in dmesg on the build machine).
L.E.: I build it from 0.
In the next days I will compile to have the last commit (it was planned anyway) and see if there are any problem.