orythem27 wrote: I tried editing out `lxpanel` as a dependency in stretch's lxde-core and rebuilt the package....
Turned out that my brain just stopped working for a moment.
Merely editing out `lxpanel` wouldn't be enough to exclude such a basic component from the dependency chain.
So, from the infomation gathered so far, OP's problem can be 99% pinpointed in the package `lxpanel`'s violation of the above mentioned lintian rule.
Putting those technical irrelevant issues aside, I must say OP has really put a lot of attention to details to reveal the possible cause of a seemingly odd problem.