@Blacksburg 

Do you use VPN on ER605?

IPsec , L2TP, PPTP, OpenVPN

I have same issue and have to use firewall from another vendor to get it to work, VPN is very buggy on TP-Link routers.

after change vpn router to another vendor the breake is off and everything work again.

  @shberge no I don't use vpn directly on the router. I did restart my server (since it hadn't been restarted in 85 days, during which my issue got progressively worse). After the restart my internet seems to be doing ok. I'll continue to monitor.

It's just frustrating because the issue can literally be anything, it's so hard to pinpoint.

  @Blacksburg 

Ok, then there is probably another problem you have, if you find a solution then it is good if you post the solution here.

I have not had anything but a lot of problems with my routers, so I had to give up and I now do VPN on a non Tp-Link router, but I use a lot of VPN so that's probably where the main problem is.

I have also some sites with very simple configuration on ER605v1 and these have worked without problems, so it varies a bit how well the routers work.

I also run an automatic reboot of everything once a week on these sites. I do not think they work very long without it rebooting regularly.