Sorry you've got no help in the last 25days... but i think i may have something for you:
Basically, make sure that traefik has full rights to read/write the /acme.json file and this is critical that the file does not exist. If it exists, but contains invalid data, traefik will silently fail. If the file does not exist, then traefik will create it w/ valid data.
Good Luck!