Ercouper Switching to x11 allowed plank to start normally.
Plasma's Wayland support makes it trivial to create a "plank replacement" that works just great. It involves creating a new panel, adding an icon-only task manager, and then setting its properties to do wht's needed. Here's what it looks like on my laptop:

There are all the options you need to do this, including one that causes the panel to avoid collisions with other windows ... just like Plank. It only takes a few minutes to figure it all out, and then it's yours forever.