Let's Encrypt SSL can't renew – no clear error

I have a server with ~5 websites, all with Let'sEncrypt that are automatically renewed.

In the last few days, one website was not renewing anymore, and I can't manually renew it!

Renewing SSl cert for https://x.com
ERROR : Cannot RENEW SSL cert !
Your current cert will expire within 15 days.
Check logs for reason `tail /var/log/ee/ee.log` & Try Again!!!

And the log suggests that I see the log...

tail /var/log/ee/ee.log
2016-11-16 20:26:37,567 (DEBUG) ee : Running command: date -d "`openssl x509 -in /etc/letsencrypt/live/x.com/cert.pem -text -noout|grep "Not After"|cut -c 25-`" +%s
2016-11-16 20:26:37,577 (DEBUG) ee : Command Output: 1480643820
, 
Command Error: 
2016-11-16 20:26:37,577 (ERROR) ee : Your current cert will expire within 15 days.
2016-11-16 20:26:37,578 (DEBUG) ee : Running command: date -d "`openssl x509 -in /etc/letsencrypt/live/x.com/cert.pem -text -noout|grep "Not After"|cut -c 25-`" 
2016-11-16 20:26:37,588 (DEBUG) ee : Command Output: Thu Dec  1 20:57:00 EST 2016
, 
Command Error: 
2016-11-16 20:26:37,626 (ERROR) ee : Check logs for reason `tail /var/log/ee/ee.log` & Try Again!!!

I already did:

• apt-get update/upgrade/etc
• deleted the entire website with site delete and created it again
• followed this instructions
• checked if "www" is set on DNS records

Running on PHP 5.6.28-1 / nginx 1.10.0 / EE 3.7.4

Thank you!