I am another user who has encountered overall very poor performance on 5ghz band Wifi connections in my brand new LG v60 since the day I purchased it. To save time and energy as I've spent more time than I should have trying to fix this issue, assume I have covered all the basics and intermediate troubleshooting.
I am aware this is a known issue caused by the Qualcomm processor in the V60 and there is a patch in the works to address it. To be clear, will this be received by T-mobile users and is there an ETA on when it'll arrives.
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