@Graven You have to reconfigure both range extenders - follow this post instructions.

@FJ04 It sounds more like a laptop's wireless adapter advanced properties need to be adjusted. Best you could do is to compare these on the other laptop and set yours similar:

@Alpine1 To configure your C50 in access point mode (bridge mode) use this guide. If you have more than one C50 daisy chained, you should set them all in access point mode.

@leoleoleoleo Follow this guide to port forward on your modem router. Make sure that your public IP address is the same as your modem WAN IP address - you may be behind double NAT or CG-NAT.

@FJ04 This could be due to a poor wireless signal on 5GHz band, but not a wireless interference. If you connect your laptop or other device with an ethernet cable to the Archer C6, this would be a...

@Whistlestop To be able to do that you'll have to configure the RE315 in AP mode - here's a guide for that. You can also refer to your RE315 user guide for this scenario - here.