Now, If you see the code you just set the SSL login to false and your issue is resolved. Also, you said that on the server there are other sites and they work fine, only this one has the issue.
The thing is maybe your site has activated the SSL from the server and from the WordPress dashboard too so the connection is secure and the site is working without any error encrypting. Obviously, the preview will appear to be fine.
This site has the SSL activated from the server but not from the WordPress dashboard that why when you set the query to force SSL login to false it works on your site so please first make sure that you have set the SSL to activate on the site from the WordPress dashboard too and your site URL is set to the HTTPS from the Dashboard >> Settings and please remove the query code that you added and check back your site after clearing the browser cache. It will solve your issue.
Otherwise, there is no need to add the query. You can simply ask your service provider “Hosting Support” because it’s their responsibility to make sure all the sites on their server will run fine. They will look into it for you and fix your issue.
