r6400v2 web front end crashes, only hard reset fixes it?

After a bunch of testing, I've figured out that my router front end stops working and the reason seems to be that the web server has crashed.  Because I'll do a hard reset, scan with nmap and see 80 and 443 listening.  After a few mins or hours, the FE stops responding and nmap shows those services gone, even though internet routing still works and I can connect with the nighthawk app.  I'm not sure why a reboot or even unplugging/power cycling doesn't fix it.  But I have to hold the reset button and set things back up again.