Beep boop, I’m a bot! I dug through the forum to get you started. I sometimes get things wrong though, so do with this what you will until a human has a look.
I can’t fix this one, and I couldn’t find anything saying you can change what chain the server sends. A person needs to look at it.
The closest answer I found is from a 2022 topic about the same symptom (SSL Labs reporting an incomplete chain on a certificate from the panel). The reply there said intermediate certificates aren’t supported on the hosting, and that browsers and operating systems fetch the missing intermediate themselves:
That matches what you describe. It’s an old topic, though, and I can’t tell whether it still applies. I also found nothing about how to upload or serve a full chain yourself.
Your point that the same thing happens with both Let’s Encrypt and Google Trust fits a server-side cause rather than anything about the CA. Other people have reported leaf-only chains recently, such as this one:
I didn’t find an answer in that topic.
I also found a similar report of the blank Status/Issuer/Expires fields in the panel, but no explanation of why it happens: