Signal strength is not the only indicator of connection. The Skybell HD needs a relatively high signal to noise ratio, effectively a very high quality signal is needed, and wifi network strength is not a quality indicator. In order to determine the signal to noise ratio and quality, you’ll need to consult your provider. They will have back-end diagnostics through Alarm.com.
An option is to dial down the resolution and test. Less data from the lower resolutions should see fewer instances of this error.