I have reproduced your use case with the HTTP(S) load balancer and the bucket following the solutions page and I could reach the object pixel.png through both HTTP and HTTPS after assigning a certificate to the HTTPS frontend.
Make sure that you have the same IP address configured for both HTTP and HTTPS frontends (target proxies) for the load balancer. If it is not the case, you should assign a reserved IP address to one frontend and reuse the same reserved IP address for the other frontend.
--EDITED according to comments
Once the frontends have been created with a given IP address, whether it is ephemeral or reserved static IP, you are not able to modify the IP address. You then have to delete the frontends from the load balancer configuration and recreate them.
When you create a frontend for HTTP for example, select IPv4 address, and then in the right scroll menu for IP address you will see “ephemeral”. Instead of ephemeral, select the “create IP address” item in the list.
A popup will appear asking for a name for the static IP address you are about to reserve.
Once you have done this, a reserved IP address is added to your project. You will be able to see it from the Cloud Console in the VPC network/external IP addresses menu on the top left pane.
You can now create another frontend for HTTPS, and you will be able to select the same reserved IP address by its name and assign it to the HTTPS frontend.
Bear in mind that if you delete the load balancer, the unused static IP address becomes free, but is still reserved in your project and is then charged as reserved, that means that you pay for it until you delete it.
Static IPs are documented at this link.
Now that you have a new unique static IP address for both HTTP & HTTPS frontends, you must configure this IP address on your registrar, GoDaddy in your case, DNS settings so the domain points to this IP address.
For the certificate, you can add it in the HTTPS frontend like it seems that you had done already.
The documentation on certificates for load balancers can be found here. You might want to check the new beta feature for Google managed SSL certicates which is detailed on the documentation page.
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what I see from the screenshot that you have sent is that you get a HTTP 404 response for your HTTPS request for "/" default path.
An HTTP 404 error indicates that the server itself was found, but that the server was not able to retrieve the requested page or file.
You are saying that it works with HTTP, what exact URL path are you requesting ?
Make sure that you have an object (image or file) that responds to "/" default path.
Or check by issuing https://yourdomain/pixel.png which is the image file located in the bucket for this solutions lab.
I hope this helps.