If there is a larger green band above your video, then likely you have switched on the SVRT (Smart Video Rendering Technology) option. You can switch it on and off by right clicking the mouse with the cursor in the fields in front of the clips in the timeline. When you do switch it on you will get additional information in intelligent SVRT. A green band means that, when you use the same output specification at production time, SVRT will give a very speedy production time. See also: https://help.cyberlink.com/stat/help/powerdirector/21/win/enu/19_01_00_profile_analyzer.html?q=svrt
IN the video clip there is a very small green line, which is the opacity line. If you point to that with the cursor a small information window will open to explain what the current opacity is and how you can change it.
There is a third green line, which shows in the yellow stripes depicting the time and frames. THIS green line tells you that the green range of clip has been pre-processed to smoothen the pre-view. You can do this by (selecting a part of the clip) and click on the render preview button under the preview screen. This feature will help you viewing the (part of the) clip after somewhat more complex editing (LUTs, transitions, many video layers and the like).
Btw: all three green lines show a slightly different tint of green (at least on my screen).

Thanks very much!
That sounds like what I'm seeing. Here is what it looks like.

Yep: Green of the third kind!

It looks like the gpu doesn’t have enough processing power for those large images on the timeline.

I suspect the same thing.