Issue could not renew Let's Encrypt - failed for <none>

[TobiasP]

I periodically receive "Could not issue/renew Let`s Encrypt certificates" E-Mails but in the mail it says:

Renewal of the following Let`s Encrypt certificates has failed:

<none>

The following Let`s Encrypt certificates have been renewed without some of their Subject Alternative Names:

<none>

if I check all the domains for this customer all the LE certs are happy and extended. how can I find out why I receive a none failed email notice?