I have a BSNL fiber connection on that some of the sites show not secure and doesn't open. But the same site works fine with the mobile internet.
For example the StackOverflow itself shows not secure on BSNL connection but working fine with mobile internet. I have tried resetting the router this problem is with all the devices I connect, I have tested it on 4 laptops and 3 phones.
The problem is the number of sites not opening on the broadband is increasing, Initially it was 1-2 sites that were not opening on Broadband but now 3 out of 10 site do not open.