Have to constantly reboot RT-AC68U

I have been struggling with this - why do I have to nearly daily reboot my RT-AC68U?

* I have Merlin's 380.62 firmware.
* I actually don't use the radio's on the router (radios off)
* I have an OpenVPN server setup for when I am out and about and want to have security
* I have about 34 household clients: Wemo/Sonos/laptops/ipads/iphones
* I have 5 Unifi AC Pro access points cat 6 wired through a Netgear switch & 2 TP link switches (all setup as unmanaged)

I have had the router for 1 month...

Have to constantly reboot RT-AC68U