@Shinoda-kl Does the flicker only happen as you are moving the divider between the main text area and NppFTP? Does it happen if you make Notepad++ a window and use the dragger thing in the lower-right corner to resize the application?
I installed the NppFTP plugin and saw one minor issue. When I move the divider line to the right there are many shadows of the divider that persistent for about 1/2 second but the screen goes back to normal. I never got the jitter that you are seeing.
I then enabled word wrap which you seem to be using and there is a slight flicker at times as I drag the divider but no jitter. That prompted me to remove or uninstall NppFTP and to instead see what happens if I make npp a window and to resize it using the dragger in the lower-right corner and moving the mouse in a circle. There is some flicker as the word wrapping does its thing but I never got into a continuous jitter state.
As times over the years I have had applications, including Notepad++ and Firefox, get into a state where it jitters much like what happens at times in your video. The issue is far more common with Firefox. It’s painting the screen and mid-way through painting the code that tries to fit things on the screen realized it’s painted its way into a virtual corner and so it starts painting again using slightly different parameters to get the text to fit, that also gets into a virtual corner and so it tries the first set of parameters again. There’s a loop of repainting two versions of the text.
It’s rare for me and from what I recall tends to happen when I’m resizing an application or the dividers. I suspect it’s an edge condition in text drawing code. The workaround is easy in that I change the size or divider by a pixel.
Reproducing on demand is not easy.
If it’s a very common issue for you and you are willing to put some effort into creating a setup that one of us can 100% duplicate then we may be able to write up steps that allow one of the Notepad++ developers to get the application into the jitter state while also trying to fully understand what bit of code has the edge condition.