@The0glitter 

If the drop-off is only happening during the peak internet traffic hours, it could be that the connection between the router and range extender is being subjected to additional interference from other devices, appliances, or neighboring networks. I would try and move the RE far closer to the Router to see if the behavior persists.

The RE220 also has a Power Scheduling Feature built into the extender. You could use this to either restart the RE on specific days or each night; that way it is not something you will ever have to actively think about.

Also, do you have high-speed mode enabled on your device? It kind of sounds like your device may have been using the 5Ghz network for a backhaul and failed to switch to using the 2.4 Ghz network as a backhaul when the traffic was congested in the evening

  @The0glitter,

Definitely please check the high speed mode on your RE, the High Speed Mode will designate a specific band for the backhaul. Since, you are already disabling the 2.4 Ghz band, you may be able to repurpose the band as the designated backhaul.