Does this happen even if you connect via network cable?
- Are your router and PC in the same room or are they in different rooms or on different floors of your house?
- Is the name of your WiFi network (SSID) the same for all WiFi bands or do the networks have different names or SSIDs for each band?
- Are you connecting directly to the router's WiFi network or are you using WiFi repeaters or range extenders?
Specify the exact model of your computer or go to Start, type msinfo and attach a screenshot of the System Information page.
Also, specify the exact model of your network card or go to Device Manager expand network adapters and post the screenshot.