Are you trying to do a dissolve? If it’s a strait cut then the first clip has handles that are still playing but a second or more is way too long. If this persists either shorten the first clip or bring it into the viewer, set your output marker and reinsert it to the timeline. You can also take the original clip, set you in’s and out’s, drag this new clip to the browser and make it a master clip. Then put this clip into the timeline.
but, before doing any of that of course, trash all your prefs.