Why is it that my wifi signal strength at home is completely good at some point, the signal strength almost always goes down in the evenings. It’s not exactly the field strength going down, but it’s sure to be much slower than during the day.
You didn't write what kind of environment you live in. Detached house, condominium, possibly panel. If you live in a panel apartment there, there is a good chance that many other people are within range of wifi, and if someone else’s wifi goes on the same channel as yours and starts using it in the evening, it can bother you.