I originally posted the problem on github but Matt Nordhoff who kindly responded asked that I post the information here.
I am simply running a routine certificate renew but the file link was not updated to the latest certificate so the webserver and postfix and dovecot all still see the previous certificate.
Here is the output of ls -alR /etc/letsencrypt/{archive,live}/
Someone or something messed up the whole symbolic linking from the live directory to the actual certificates and private keys in the archive directory.
This shouldn't happen. Most likely someone manually changed the symbolic linking in an attempt to correct something.
Anyway, with the creation date you can see the correct files are timestamped on July 10th at 17:00 with number "2" in the archive directory www.spots.school. But the symbolic links in the live directory of www.spots.school are linking to the wrong archive directory (www.spots.school-0001). And thus the incorrect files.
Also, it shouldn't happen that certbot renews certificates to a number "in between" currently existing certificates. It should count upwards, so it should have generated files with the number 6. Perhaps someone deleted the number 2 files manually?
I think that's normal with this issue. It used 2 because the live symlinks and/or the archive-0001 files used 1. It's properly incrementing the wrong thing. Or the right thing, depending on how you look at it.
Configuration file seems to be OK, only the symbolic linking in /etc/letsencrypt/live/www.spots.school and the file numbering in /etc/letsencrypt/archive/www.spots.school seems to be off.
My advice:
Delete the files cert3.pem, cert4.pem, cert5.pem, chain3.pem, chain4.pem, chain5.pem, fullchain3.pem, fullchain4.pem, fullchain5.pem, privkey3.pem, privkey4.pem and privkey5.pem from the directory /etc/letsencrypt/archive/www.spots.school (this step might be skipped, but I have no idea if the next renewal will go without any hitch if you let them exist…)
Remove the entire directory /etc/letsencrypt/archive/www.spots.school-0001 (it isn’t usedcertcert anyway)
Go the the directory /etc/letsencrypt/live/www.spots.school and make the correct symlinks: