Just completed an installation of fedora 30 LXDE, and had issues with copy/paste. @stephenadler, I’m assuming you’re in the Workstation, but maybe my solution will give you a hint. I clicked the clipboard icon on the lxpanel:
under Settings, deselect Capture hyperlinks only
under History, deselect Purge history after timeout or select a different Timeout seconds (mine was set at 1)
I copy/paste tested in midori (webbrowser), gedit, xterm, lxterminal, vim, emacs.
As @happycat00 pointed out, the solution might be that simple. Like taking your vehicle to the mechanic because of a loud screeching noise - which he can’t solve - only to find, when arriving home, that the pet cat is missing.