I encounter the same problem as the user has in this post: Why does Samsung Android browser say our site has a valid certificate, but the site identity has not been verified?
The accepted answer is:
I don't think you can do anything about it but to upgrade your Android.
The problem here is a generic top-level domain .vip and older Android versions do not recognise them as public (hence the "a name valid only within your network" message). It's a known problem and Wikipedia lists it as one of the technical issues with these domains.
With Internet app version 4.0 on Android Marshmallow, your certificate is verified properly.
'Upgrading your android' means I should get a new mobile phone?
Some facts about my device
Application version: Chrome 73.0.3683.90 Operating system: Android 6.0.1 (Marshmallow), SM-G900F Samsung Internet: Version 9.2.00.70
edit: status: not verified properly, obviously due to applications are unable to pull the cert info from the system trusted store?
Anyone know where I can find more information about this? Installing the certificate in the user store works but shows a network may be monitored warning message which I guess I have to live with it.