Reporting bugs before Ubuntu releases has never worked for me. They always land a bunch of major changes after the supposed "freeze" then they ignore all feedback because of the freeze. It's infuriating.
To get a response on a buggy GNU coreutils patch of theirs [1], I had to mention it in a rust-coreutils bug months later...
[1] https://bugs.launchpad.net/ubuntu/+source/coreutils/+bug/215...
Maybe the bugs get traction if you have a service contract?
Best to file bugs directly to upstream, but that of course means you should try it on the latest upstream version and not whatever version ubuntu ships, so it's more friction.
But if you can identify it as a bug in a version in Debian, that's a good place to file, as Ubuntu will get the fix eventually.