After entering commands from here Swap file not mounting on boot (I used it for one drive, it gave bad i/o error.), the drive contents are destroyed and while using SSH connection with PuTTy, it advised me deleting contents of (possibly only files in, i remorse) /overlay/upper, but I deleted all folders in it. Possibly because of that, the device became like it reset.
Until then, even after hard and soft resets, the device doesn't accept any passwords on LuCI, although I set one on PuTTy, including the default password root.
Is the only option to survive from this reverting back to stock firmware and starting from scratch?
Note: My drive was partitioned as NTFS, so /dev/zero command option is for ext partitions. That might cause the problem...