I had the same problem. Apparently there is something wrong with tplink's firmware or the tftp recovery progress, that corrupted one or some critical partition ("tplink" in my case).
If you don't want to throw it away or build anything, thanks to this post, you can follow the normal Installation via UART guide on device wiki, only change the last step, from reset to bootm 0x9f030000 , like this:
Ath> tftp 0x81000000 openwrt-18.06.1-ar71xx-generic-archer-c60-v2-squashfs-sysupgrade.bin
Ath> erase 0x9f030000 +$filesize
Ath> cp.b 0x81000000 0x9f030000 $filesize
Ath> bootm 0x9f030000
This will skip the factory boot check integer partition, but you have to repeat this every time the power goes out.