I've experienced this quite a few times but mostly on wifi. 3G/4G networks I always attribute it to bad cellular signal.
What usually happens, for me anyway, is that when I'm connected to a dual band router or a router with Smart Connect turned on, my device will be automatically connected to a 5Ghz wifi. 5Ghz signals do not go through walls very well, because of shorter wavelengths so I typically force my device to connect to a 2.4Ghz network. However, this also depends on your wifi, if you have plenty of devices connected to a 2.4Ghz network such as dvr, dvd, tv, printers, thermostats, etc, the network could also be congested that it might be better connecting to a 5Ghz wifi, but in my experience, there are more dropped signals in 5Ghz compared to 2.4Ghz.
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