OpenVPN stops all traffic on Ethernet after ~60minutes

Good moing, I'm hoping someone can help me with solving a very frustrating issue.

After having my inteet coection snooped on more than one occasion, I have started using a VPN to encrypt my traffic. However, after approx 60 minutes, all my traffic will stop abruptly. I have spent the last 5 hours trawling the inteet to find a solution but nil joy.

My setup is as follows:
Ubuntu 16.04 LTS
ASRock mini-itx motherboard with Etheet built in
Linksys wrt1900ac
The computer is coected to the router via a 1gigabit cable.

I have installed the OpenVPN packages and are managing my settings via the gnome network manager.

The VPN coects fine and will work as per normal (including an IP check) until approx 60 minutes, then all traffic stops. The only way to get traffic working again is to either discoect the VPN (not desirable) or restart the machine (where my frustration lies as I am in the middle of working).

Self fix #1 - Initial searches indicated it might have been a DNS issue from my ISP, that it was blocking access because I was using a VPN. I changed my DNS to the DNS.watch no logging servers on both the network coection and VPN, rebooted, but this did not fix the issue.

Self fix #2 - Another search indicated it may have been a firewall issue, so I ran the remove command for both firestarter and ufw, rebooted, but this did not fix the issue either.

Self fix #3 - I tried the option "apply to traffic on this network only" but that results in everything bypassing the VPN.

I can't see how it's the VPN though, as I tested it on my Android phone and it does not drop out or stall at all. I can't see it being the router either as all my other devices are working fine.

The only skerrick of an idea of where to head next is the IP tables, but I would have no idea where to start, and I'm at my wit's end already.

Advice please? Thanks in advance.