I have been using a WNDR3700v4 for several years, with its outsized RAM and NAND flash. I paid about $15 for a used one on eBay. It worked flawlessly until recently, when my WiFi became unstable and soon was completely inoperative. Reboots, power cycling, unplugged, nothing brought back the WiFi functions. I figured some chip wore out, so I ordered another cheap used WNDR3700v4 on eBay. I also could not resist buying another unit, listed as bricked, for $0.99 plus shipping. The "bricked" unit came up immediately as DD-WRT, go figure. So I backed up my working configuration, used tftp to load OEM firmware to the two newly arrived routers, flashed the latest OpenWRT, and restored my configuration. Both newly purchased units worked perfectly, including WiFi.
So I did the same thing on the failed unit - tftp flashed OEM, flashed OpenWRT, restored configuration from backup. And it now works perfectly, too.
Does the flash in consumer routers flip a random bit from time to time? Is the unusual NAND flash on these units more susceptible to subtle corruption? They are a great OpenWRT router for the low used prices. Someday I may load the special build that makes all 128MB of NAND flash available.