What is your operating system?
What is your Shotcut version (see Help > About Shotcut)? Is it 32-bit?
Can you repeat the problem? If so, what are the steps?
When zooming in, cutting a small part and removing it with X, there is a delay(lag).
If you cut with s, zoom in, select with the mouse to then zoom out and press x, removal is almost instant(selecting with the mouse when zoomed in is not).
If you cut with s, zoom in, select with the mouse to then not zoom out and press x, removal is much delayed.
Whatever you do, it takes significantly more time when zoomed in. Even though in the case of x the same amount of data is removed, it takes much longer when zoomed in.