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I would make contact with D-Link support about this. Possible faulty router.
Try disabling auto channel and manually select channels like 1 6 or 11 for 2.4Ghz radio and 5Ghz 36, 40, 44, or 48. It s best to install something like a wifi scanner app on your phone to determine the best channel that is not in use in the area
So is there any other neighboring wifi signals near by? If so, how many are there?