My Site Suddenly Returns 526 (Invalid SSL Certificate)


Today, my site suddenly returned 526 (Invalid SSL Certificate), even though the certificate is still valid:
Found the following certs:
Expiry Date: 2019-04-29 15:09:42+00:00 (VALID: 55 days)
Certificate Path: /some/path/fullchain.pem
Private Key Path: /some/path/privkey.pem

Cloudflare’s SSL setting was usually “Full (Strict)”, and origin’s SSL certificate is provided by letsencrypt.

I had to change the SSL setting to “Full” to make it work again.

Anyone has any idea why this suddenly happened? Thanks.

My guess would be the certificate expired. You said it still is valid, but are you referring to your certificate or Cloudflare’s?

Whats the domain for starters?

Hi Sandro,

Thanks for the prompt reply.

I was referring to my site’s certificate (letsencrypt).
The domain is “”.


In that case the certificate shouldnt be considered invalid.

Would you feel comfortable to reveal your server’s IP address here?

You can delete your posting now if you wish.

The certificate returned by the server expired two days ago. That explains the 526. Have you recently renewed the certificate?

May I know how to check that?

I had force renewed before I changed the SSL setting to “Full”.

Now the validity is until:
Expiry Date: 2019-06-03 04:03:13+00:00 (VALID: 89 days).

Even though it is renewed, whenever I change back the SSL setting to “Full (Strict)”, it returns 526. Does it mean the certificate was not actually renewed?

Did you restart the service after having renewed the certificate? Maybe it is still using the old one.

Oh my, I forgot to restart the web service. It is OK now.

Thank you so much for the help and for your time.

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