Internet Drop Outs

I was having the same problems with 2 routers. One a Dlink 822 and the other a Tplink C7.
We replaced the 822 with the C7 as we thought the 822 was failing. It was just past warranty when it started to disconnect, extremely slow speeds etc. Rebooting or factory resets seemed to cure the problems briefly, for maybe an hour or 2. When connecting directly to the internet through the modem the connection was excellent so we figured the 822 was failing.
We replaced the 822 with the C7 and were amazed at how well it worked. That lasted 4 months and the same problems began. I monitored the connection with Windows Task Manager Networking Utility and it never showed any disconnects although it did show the speed drop to zero regularly, sometimes it would pick up the signal again but often it would not and either required me to open another browser page or reboot the router. Once again connecting to the internet directly through the modem gave us a stable connection. Ping tests worked fine, speed tests were a mixed bag.
I contacted Tplink support they responded in less than 2 days for my first contact and within in day on other contacts. They were trying to help but could find nothing wrong and bumped my concerns up to their engineers.
In the mean time the connection became so bad we reconnected the 822 and it worked flawlessly for about an hour then the problem started again. Although this time the Windows Network Utility showed our network connection disconnect briefly and attempt to connect to our VPN network connection whereas the C7 always showed our network connection as connected and the VPN connection as just another network connection with no activity or connection. The VPN was not connected and the VPN software was not running. The 822 would always pick up our network connection after each attempt to connect to the VPN connection whereas the C7 seemingly did not. But speeds were extremely slow.
I disabled the VPN network connection with Windows Control Panel\Network and Internet\Network Connections and the problem disappeared. Connection was excellent for the rest of the day with the 822. We reconnected the C7 today and have had no problem.
These problems were very evident while streaming video and when they were at their worst sites would load VERY slowly or we would get a message that there was no internet connection.
We now question if the Dlink 822 was in fact failing or was a victim of the VPN network connection. We still can't figure out why the C7 worked flawlessly for 4 months then started to act up as the VPN network connection has existed for several months to a year. We seldom use the VPN connection as it does not provide us with any benefits and I will likely uninstall it.
Hope this helps.