I just had a similar issue going from 4.2 to 4.2.1 and followed the same directions, it seems to be working here also. I received this message:
[i] FTL Checks...
[✓] Detected ARM-hf architecture (armv7+)
[i] Checking for existing FTL binary...
[i] Downloading and Installing FTL...curl: (56) SSL read: error:00000000:lib(0):func(0):reason(0), errno 104
[✗] Downloading and Installing FTL
Error: URL https://github.com/pi-hole/FTL/releases/download/v4.2.1/pihole-FTL-arm-linux-gnueabihf not found
[✗] FTL Engine not installedUnable to complete update, please contact Pi-hole Support