Interesting bug observed in 19.07 by users of some routers: the unit will perpetually boot into failsafe mode despite not being triggered to do so. Recompiling with the failsafe module removed from the build solves the problem, but exposes what is possibly the root cause - configuration changes remain only as long as the router is powered on despite being saved, nothing persists through a reboot of the router, and the unit will always start up with the default config.
I had to test it on my (deprecated) Netgear EX2700 and could confirm the exact same problem. Other than the lack of configuration persistence, 19.07 performs just great and I was pleased with many of the new features and changes. Unfortunately I'll have to stick with 18.06.6 as I have power outtages every now and then.