Yes, this can happen with a Leica to. 3 weeks ago on the banks of the very fine river the VIGE in France, wile changing film rolls, the shutter stoped halfway open (or close). Noting could help, no shacking, no turning the speed dail, no cocking the shutter, noting helped. Till I got home and , by coincidence I gently touched the shutter curtain thru the lens opening and, click, it worked again! In the main time I went on shooting with the other M5 I was carrying. But not on the right film. One is always loaded with APX 100 and the other with Tri-X or APX 400. After what happened I did not tempted to change the film roll (from Tri-X into APX 100) on the river bank.
Yes, "..het kan verkeren.." said Bredero, the famous Dutch writer.
Good luck,
Philippe