Why doesn't https work from mobile devices?

Question

Nginx

certificate from comodo. from the computer everything is fine, but from mobile devices it says that the connection is not secure

Answer 1

ssllabs.com/ssltest/
What does it say about your site?
Run it, look at the results, look at Handshake Simulation and what about mobile OS, for example.
If everything is fine, then your mobile provider may be intercepting https and replacing certificates.