It would really help people to help you if you listed:
- The speciifications of your computer;
- The operating system you are running on;
- The version of Shotcut you are using.
- the details of the file you are editing (I use mediainfo and cut and paste from the menu item View->Text.
A screenshot of the whole Shotcut window showing in particular the timeline and the filters panel is also useful. See also the suggestions made here: