These I can answer!
Chrome 39 on Windows and Mac, Safari on Mac. All experience the same issue.
I have tested with self-signed; works fine (with the exception of the warning you have to get past).
Works fine without https enabled; this is how I'm using it now.
I can't ask my cert provider about the error because I can't find what webserver it is that's embedded into deluge-web. I can't ask Namecheap (the reseller I bought the Comodo cert from) why my certs don't work with deluge-web; they have no idea what the underlying technology is.
I searched for the error, but there were no suggested fixes mostly because the error is so cryptic and limited.
Comodo's support site explains how the root and intermediate certs are cat'ed together with the domain cert for their UCC product (which is what I own), but when I did this, I got the error you saw.
https://support.comodo.com/index.php?/D ... termediate