Wifi is very odd and unpredictable. I have a Belkin router/modem. My desktop is connected to it with an Ethernet cable and we have three other computers in the house. The closest is in my son's study, it's less than 5 metres from the router, and has an internal wall to go through, and is not line of sight. There are no variables, but the signal on his computer varies from 0 to full strength, and there is no clear pattern of it being better during hours of light or darkness.
I often use my laptop on the balcony, there are 4 walls for it to go through and again it is not line of sight. The signal is fairly consistently 2 or 3 out of 5 on the indicator, but sometimes, for no obvious reason, it is impossible to get a signal there.
Sometimes I move into the lounge if it gets cold outside and the signal there is worse than on the balcony, yet it is closer to the router and there is one less wall for the signal to go through.
Make sense? Not to me.