Since, we got so many support tickets about this already 🙂 I will paste what I said in the other thread.
Let's Encrypt have started using R3 as the intermediary cert - https://scotthelme.co.uk/lets-encrypts-new-root-and-intermediate-certificates/ . This cert has issuer text slightly different. Since the text has changed, Cloudron tries to renew the certs too early and this results in the above notification. The notification can be ignored since it's a false alarm, the certs and sites will be fine.
There are two ways to fix this:
Update to Cloudron 6 - you can go to Settings -> Check For Updates and then Update. It will give a notification that it is unstable. It's reasonably safe to update, the notification exists because we roll out updates very slowly to keep support manageable for us. Please expect some downtime (like 10 mins) since the update re-configures all the docker containers.
Alternately, you can make this one line change in your current Cloudron version - https://git.cloudron.io/cloudron/box/-/commit/3e62f1913ab05750a343c197c519d38bf17d5b3b . The file is /home/yellowtent/box/src/reverseproxy.js and then systemctl restart box.