Stutter in Shotcut preview is commonplace. There is no way to eliminate that 100% with the potential heaviness of video processing required. Otherwise, without much video processing (there is likely always some hidden processing), when playback goes to the next clip, it might need to be reopened because not all clips in the project are held open to prevent exhausting resources (memory, file handles). There is buffering to mitigate that, but it may be defeated by the cost of reopen. Did you export and experience stutters when played in your media player? If so, see this thread: