acme.sh no longer writing well-known file

[ebonweaver]

I have been using acme.sh on 3 servers for some time. Suddenly it no longer works for unknown reasons on one of them. The renew fails due to a 404 looking for the challenge file in .well-known/acme-challenge/, because that folder does not exist. This is rather puzzling.

1. If that's always where the challenge file is written and it worked multiple times before, why is that folder no longer there?
2. Why is the script not creating the folder and file?
3. That folder isn't on any of the other servers where it works fine, so... huh?
   It says to look at the log for more details, but there are none after the 404, but the above makes no sense anyway. There is no log on the other servers where it's working... only get log if failure?
   I do see in the log where it says it's writing the file to that location that doesn't exist, so that's clearly wrong as it should indicate it failed to write the file and why.
   Any ideas what is broken here?

[ebonweaver]

The only difference I can find between the working and broken systems is the http.header file in the .acme.sh folder is quite different from the other two:
Content-Type: application/json
instead of:
Content-Type: application/pem-certificate-chain
and two lines the other two don't have:
Boulder-Requester: 889452907
Location: https://acme-v02.api.letsencrypt.org/acme/chall-v3/253254538326/hvh1QQ
Also the second "link" line ends in rel="up" instead of rel="alternate"

Unfortunately I have no clue what any of this means, but hopefully since this file seems to be created every time a cert is renewed, and these lines are the only thing different, someone here can spot the problem and advise a solution.