I am able to crash Shotcut 20.04.12 consistently when adding multiple mp4s from the playlist to the timeline using the Playlist “Add selected to timeline” option.
Though perhaps a coincidence, the crash occurs when the source window is active and its content is paused within the clip. When the cursor is at the 0:00 position or (on reload after the crash) the source window inactive, the timeline loads from the playlist without a problem.
I am running Windows 10.0 Build 18363 on a Dell Inspiron 15-3567