From what your screenshot looks like, you’re are zoomed in at the frame level. Depending upon your Video Mode, you may not be able to establish a transition at the exact location you desire.
To see what your video mode is set to, click on Output (located above V1 in your screenshot), then click on Properties. Example if your video mode has a fps rating of 24.9260323, you will get that random point as your talk about. If you video mode is one and you have video footage that is different, then there may be additional problems because of mixed video fps.
Shotcut has a conversion tool for edit friendly, which basically makes a new video file from your source, leaving your source intact. Click on a clip, then Properties, at the bottom there a convert button. The conversion tool is extremely helpful for cell phone videos, which most likely will have a variable FPS.
Again, I’m only guessing here, but if you left your Video Mode in “Automatic” you may have that odd fps. There is a number of presets already made up for Video Modes to pick from.
From your screenshot, not sure how far you are wanting to move your clip.
This section I have highlighted in green is just a mere 5 frames.
I don’t know exact length of your video, and only basing my best guess on how the audio waveforms look zoomed in.
