Certificate is valid on desktop platforms and fails on Mobile platforms

[aassalslv]

When visiting the website on a mobile device, it gives me an error that my connection is not private. On desktop platforms it works perfectly. When analyzed my domain with SSL Server Test (Powered by Qualys SSL Labs)

I get this

My domain is:
https://cdn.sightline.se/1516e534977e1959/psw/Spinneriet/

My web server is (include version):
IIS 8

The operating system my web server runs on is (include version):
Windows Server 12

[webprofusion]

Hi, please see Let's Encrypt DST Root CA X3 expiry Sept 30th 2021 | Certify The Web Docs for Windows related guidance.

Your first step is to reboot your server, but you may need other steps such as installing the ISRG Root X1 certificate. You can avoid rebooting by editing your https bindings, but a reboot is easier.