Well I never use the panel as it just seems to get in the way.
But I tried your repro and can’t confirm as actually the panel remains open when a project is closed and re-opened.
If you actually quit Cubase it will be lost…but it takes one click to re-open and you only need to do it once on opening Cubase, so is hardly an issue.
EDIT…sorry slightly misread your post…my panel always opens in the same position once I have positioned where I want it.