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I did use erase_flash with no observed difference.
To rule out some of the obvious;
To confirm, your development chip is an ESP8266-12 and are you developing on the Windows 10 platform?
Might be down to a PC reboot, although I did cold start yesterday.
To me still appears to be new firmware that is causing issue, as boot_v1.6.bin is newer than that 1.4 in flash instructions.
My command string is very similar. Have you run
erase_flashas suggested? That wipes everything and is a good idea when moving between versions.