When I run Claws Mail in Plasma and Wayland on openSUSE Tumbleweed, dragging a message from the message list to a new folder causes Claws Mail to freeze for several seconds. Once I start dragging a message, the mouse pointer changes to a hand icon. Dragging this pointer over a folder in the folder list doesn't result in that folder becoming highlighted. If I release the mouse button anyway, the pointer remains a hand icon for a while (say, between 5 and 30 seconds) before the message actually gets moved. During this time, Claws Mail is completely unresponsive to further input. If I then try to close Claws Mail, it (and sometimes Plasma itself) crashes. The problem doesn't occur when running Claws Mail in Plasma and X11.
Works fine here.
Confirmed; I can no longer reproduce the problem either (now running Claws Mail 4.1.0). Guess I can switch back to Wayland from X11.