There are several possible reasons why the padlock icon may not be visible when accessing a website using SSL. Here are a few things you can try to fix the issue:

1. Check the SSL certificate: Make sure that the website has a valid SSL certificate installed, and that it is issued by a trusted certificate authority (CA). You can check the certificate by clicking on the padlock icon in the address bar of your browser and looking at the details. If the certificate is expired or invalid, you will need to renew or replace it.
2. Check your internet connection: Make sure that your internet connection is stable and working properly.
3. Clear your browser's cache and cookies: Clearing your browser's cache and cookies may fix issues related to SSL certificates.
4. Disable VPN or proxy: If you are using a VPN or proxy, try disabling it and accessing the website again.
5. Update your browser: Make sure that you are using the latest version of your browser, as older browsers may not be able to access websites using the latest security protocols.
6. Disable browser extensions: Some browser extensions can cause conflicts with SSL certificates. Try disabling your extensions and see if that fixes the issue.
7. Check your system clock: Make sure that your system clock is set to the correct date and time, as SSL certificates rely on this information to verify that they are valid.
8. Inspect the page for mixed content: SSL encrypts the connection to the server, however if the page is served over https but some resources (such as images, CSS and JavaScript) are served over http, it will throw mixed content error and the padlock won't show up, check that all the resources are served over https.
9. Contact the website administrator: If none of the above steps fix the issue, contact the website administrator, and let them know that you are not seeing the padlock icon when trying to access their website. They may be able to help you resolve the issue.
10. Check with your IT admin: If you are facing this issue on a work/corporate network, you might want to check with your IT admin as there might be some internal policies blocking you from accessing the site or some kind of SSL scanning that is breaking the SSL connection.
11. Check if the Port 443 is open at Firewall to allow https traffic and on web server - https://ping.eu/port-chk/