Huh, the environment variable thing was specifically aimed at acme.sh which rather arbitrarily changed the config value from ACMEDNS_UPDATE_URL to ACMEDNS_BASE_URL, never acknowledged this in a changelog and then silently failed after an automatic upgrade as recommended by the default install:
Ah, I plausibly didn’t hit this because I was permanently on a fork of the acme.sh codebase, after I opened a PR to support Route53 subzones and it was ignored.
https://github.com/acmesh-official/acme.sh/commit/2ce145f359...
It's also cleared out my .account.conf files when run on the suggested cron.
I've started using updown which also monitors my TLS certs simply because I no longer trust the process to work as documented.