Clipping after export on each video

I have DL videos from YouTube and they are full length on Shotcut they are full length but when I export them to get a combined full-length video they are each shortened by a couple of seconds (but they are combined)… what am I doing wrong?

Are they your videos, if not do you have written permission from the channel owner to copy and edit their content?

"You shall not copy, reproduce, distribute, transmit, broadcast, display, sell, license, or otherwise exploit any Content for any other purposes without the prior written consent of YouTube or the respective licensors of the Content."