When starting a plasma wayland session, krunner is only half-loaded. "Alt-F2 kons" in this state results in either "s" or an empty krunner prompt. Successive invocations work fine. Probably easiler to reproduce on a slower machine, but I get a 100% failure rate in a VM. openQA found that even keypresses after krunner is shown completely get lost. Workaround: "krunner -platform xcb".
*** This bug has been marked as a duplicate of bug 385693 ***