Thanks.
I got exactly the same as you, as far as I've got. But I'm going to describe it anyway, for emphasis:). Downloaded the snapshot eu factory bin (lede-17.01.4-ramips-mt7620-ArcherC50-squashfs-sysupgrade.bin) on 5 Jan, plucked up the courage to upgrade today using the TP-Link web interface; the upgrade was accepted and on reboot the device stuck cycling the LEDs through power/internet (amber)/all.
I thought that was it (I'm not going to be doing any soldering, that's for sure), especially after trying the TFTP method and getting no result. Not entirely helped by my network cable not always being perfectly well seated.
I made the same error with the file name, trusting https://wiki.openwrt.org/toh/tp-link/archer-c50, which has the typo with the case of 'V'.
Eventually, with my cable seated correctly, I checked syslog (no systemctl on my laptop yet) and could see that the device was trying to fetch file ArcherC50V1_tp_recovery.bin. Surely the name I was already using, but what the heck, let's try renaming my TFTP file. Bingo. Device comes back up with solid green lights.
That's as far as I've got for now (after checking I could get back into the web interface). Time to take a breath before deciding whether to press on.