What’s different about your setup? Do you filter electricity with an uninterruptible power supply? Cable lengths? No other equipment nearby? Good ventilation?
I have a pair of TP-Link WDR-3600s. Both run OpenWRT "Barrier Breaker" and they've been rock-solid. One is on a filtered UPS (the main router), but the other one is just plugged into the wall and usually has a loaf of bread on top of it (the wireless relay in the pantry). Both have been fine, so I don't think it's the power supply.
I currently have a TD-W8960N that's been running 24/7 for about 3 years. Only a couple of outages which were due to ISP issues. Ventilation is nothing special, its just sitting on a shelf. No UPS, but the power board its plugged into does have some limited amount of power spike filtering I believe. Cable length from modem to phone socket on wall is less than 50cm. It shares the socket with an ADSL2+ line filter splitter and a standard telephone. Got about 10 WiFi devices in the house sharing access.
