my guess definitely would be network problems. A fridge often has a metal casing around it and that works like a Faraday cage, which would block all communications. There will be small leaks in the cage that allows part of the signal through. You reported good signal strength with the better antenna’s but is that both ways? What is the signal strength at the other end? is that with the device in the fridge?
Is you 2.4Ghz network on a different name than the 5Ghz? I don’t know, you router might be trying to switch your device to the 5Ghz network when it is using the same name.
… just some thought that might get you going, but that also might be totally irrelevant.