Created attachment 4366 debug info I've seen that reproducible crash on the two boxes where i had actions plugin to only show one button. One one computer, removing action button made migrate succeed. Once with pre1 and once with pre2. I can do live debugging and provide .config/xfce4 snippets this afternoon but in the meantime here's gdb trace of migrate.core & prints.
I think this is fixed in 25d6c24.
Confirmed working, my action button is back to showing only the logout dialog button, and migrate didnt crash this time. thanks!