Let's encrypt certificate renew failed for subdomain

My YunoHost server

Hardware: VPS bought online / Old laptop or computer / Raspberry Pi (specify version, 0 to 4) at home / Internet Cube with VPN / Other ARM board / …
YunoHost version: x.x.x
I have access to my server : Through SSH | through the webadmin | direct access via keyboard / screen | …
Are you in a special context or did you perform some particular tweaking on your YunoHost instance ? : no / yes
If yes, please explain:

Description of my issue

Yunohost is not able to have the Letsencrypt-cert renewed for one of my subdomains. Perhaps others will give a problem later as well, but so far this is the only one. The issue has been going on for a couple of weeks. I have not been able to resolve the problem:

Error: Wrote file to /var/www/.well-known/acme-challenge-public/SeuSwtkXgB9L2j6TbWaky1eWbEHG-pr3RgmP2rbwRhc, but couldn't download http://sub.domain.tld/.well-known/acme-challenge/SeuSwtkXgB9L2j6TbWaky1eWbEHG-pr3RgmP2rbwRhc: Error:
Url: http://sub.domain.tld/.well-known/acme-challenge/SeuSwtkXgB9L2j6TbWaky1eWbEHG-pr3RgmP2rbwRhc

Checking the .well-known dir, the file is there:

 ls /var/www/.well-known/acme-challenge-public/
7ChXW_0YPT2Hq4CuYONsC-ndIE3IjYImzSi4f-d0xmw  SeuSwtkXgB9L2j6TbWaky1eWbEHG-pr3RgmP2rbwRhc

Even so, visiting the domain returs an empty page:

Any idea what could be the problem? I tried:

  • running the renew-action manually
  • also after restarting nginx
  • also after manually removing stale files; it will recreate a file with the same name
  • just waiting and hoping

I think that if I troubleshoot enough, I might hit the LE-rate-limiter. So far, I did not try more than a handful attempts per day.

The log of the last manual renew action is at https://paste.yunohost.org/raw/imegogugas