Had same issue. Believe it's caused by acme.sh now defaulting to ZeroSSL instead of LetsEncrypt. Tried registering acme.sh ZeroSSL email, but still wasn't renewing.
Tried changing acme.sh back to letsencrypt (didn't help either. with expired domains at least, might help with future renewals):
/root/.acme.sh/acme.sh --set-default-ca --server letsencrypt
Had to go into the config file (/root/.acme.sh/cwp_certs) for each domain that was failing and change
Le_API='https://acme.zerossl.com/v2/DV90'
to
Le_API='https://acme-v02.api.letsencrypt.org/directory'
then run the cron again
/root/.acme.sh/acme.sh --cron --home /root/.acme.sh/cwp_certs --renew-hook "systemctl reload postfix dovecot"
it now works!
Not sure if I should look into trying to get ZeroSSL working. But LetsEncrypt seems to be working fine...