What Hardware version is your router? Look at sticker under router.
What Firmware version is currently loaded? Found on routers web page under status.
Some things to try:
urn on DNS Relay under Setup/Networking.
Setup DHCP reserved IP addresses for all devices on the router. Setup/Networking
Ensure devices are set to auto obtain an IP address.
Set Firewall settings to Endpoint Independent for TCP and UDP.
Make sure uPnP is enabled under Advanced/Networking if you have this option.
What wireless modes are you using?
Turn off Short GI and Extra Wireless Protection if you have it. Under Advanced/Advanced Wireless.
Maybe someone can review your router settings with you using
teamviewer.