Computer Help and Support

You may have a neighbor with a new wap that is stepping on yours. It may not be signal strength but relative signal strength.
The 2.4Ghz band is cramped, so in multifamily buildings and snug neighborhoods agreeing to a few simple rules are important.
1. Only use bands 1,6 and 11
2. Only use 20Mhz bandwidth, not 40

All this can be verified with a wifi scanner app such as WiFi Analyzer. This will allow you to see all your neighbors wifi signals. This way you can see who is on what channels and how close they are. Then you can decide which of those 3 channels is best for you.