Insecure connection warnings while domain validates

For our websites we use Let’s Encrypt to generate the SSL certs. One of our clients however has issues when he visits websites secured with a Let’s Encrypt SSL certificate. We cannot reproduce the issue, and when we validate the installation of the certificate using NoPadlock, all seems fine (Report here

Our guess is that the client is using a Citrix(-like) environment in his office and it could be an internal firewall issue. Has anyone experienced a similar issue? We want to help the client and his system admin to figure out the source of the issue, but I haven’t been able to find anything related sofar.

My domain is:

The client sees an Insecure connection warning in Chrome

My web server is (include version):

The operating system my web server runs on is (include version): CentOs 7 with Plesk Onyx

My hosting provider, if applicable, is:

I can login to a root shell on my machine (yes or no, or I don’t know): no

I’m using a control panel to manage my site (no, or provide the name and version of the control panel): Yes

Hi @sanderdewijs,

Can the client provide a screenshot of the error they are seeing?

Usually when there is a middlebox/internal firewall meddling with the HTTPS connection you can examine the certificate details in the browser and this will often show a non-LE certificate that doesn't match the server certificate.

Hi @sanderdewijs


The client should use CTRL + Shift + I to open his Chrome console.

There should be some mixed content warnings with links reported.

And the Security Tab shows the details of the certificate.

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