I did a little more investigation, and unfortunately it turned out that many people using the same wireless card as your device has (Qualcomm QC9377) have the same issue - dropping connections or no connection at all 
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Nobody currently has worked out a stable solution yet. Some people reported success when configured their internet router to use a 2.4 Ghz channel width of 20 Mhz, so eventually this may work for you too. Please note that not all internet routers let you configure this and it may be hidden somewhere deep inside the configuration interface if it is.