Nethserver stops working over night

first of all: is your server RHEL7 certified?
did you add anything on HW side?
did you check your ram?

then… you can always download and install manually an older kernel and try booting it…

I won’t use a unsupported non official kernel on a production server

Finally, if nothing work as expected, I’d try the virtualization way, i.e. NS as a VM

The server is a Dell T130 and is RHEL7 certified. This is an officially CentOS confirmed bug.
Indeed virtualization is a solution I would go for, but as a last resort.
Anyway when 3.10.0-820 version is released I would go back to it if is possible. Is it?