I am running OpenWRT (The latest formal release) on Netgear R7000.
I am using a Wireguard VPN.
This VPN is dropping regular and the only solution is to reboot the router.
What is causing this. Is this a bug in OpenWRT..
What can I do to solve this..
Very likely, one side or the other is experiencing a change of IP addresses. If you're connecting to a commercial VPN, this wouldn't happen on their side, but could be your side if/when you DHCP/PPPoE based IP address changes. If you're connecting to a peer that is using a dynamic IP (again, DHCP or PPPoE), that side could also be implicated.
If it is as I described above, no, not a bug.
There are a few ways of handling this situation, but one of the easy ones is Watchcat. If the tunnel stops working, simply performing an ifdown/ifup of the WG interface should usually fix that problem.
Your problem description doesn't really allow to draw any conclusions, in the absence of magic crystal balls. You will need to debug what is happening, before we may find out why it is happening, what's to blame and how to avoid/ fix it.
While psherman is raising one potential cause, there could be many others as well (e.g. OOM (despite 256 MB RAM), crashes (Broadcom is not a primary target for OpenWrt), various connectivity issues (on your- or the remote end), misconfiguration (routing- or gateway addresses changing due to spurious dhcp renewals), etc. pp.). Start by reading logs (logread ; logread -f), what happens at the time you're experiencing connection drops - and explain a bit more about the remote end (private VPN, work VPN or commercial VPN provider).