Can you describe the problem a bit more. I'm not quite understanding what you are seeing exactly.
Or, if you could post a short video that shows the issue, that would be great.
he means the issue I have too, wrote u an email right now:
Hope you all are well in 2018!
With the last updates (think 1.5 or even 1.4) there is now a very, very big issue with the video editing.
When every using a slow mow video and reducing the video speed of a clip, everything works fine. But if you then zoom in at the beginning of the clip and make a second zoom out by the casual framing with two dots (one at the beginning, one at the end), the video is lagging. Regardless the codec, regardless the video speed (except normal speed or faster), regardless the kamera taken with, regardless the format.
This was definately NOT there before 1.4.
I mean, of course I could export the video without framing the zooms of the slow mow scenes and re-import and do it then again. But this doesn't makes sence regarding working time, space, additonal project and especially regarding convinience.
Please try it and fix it as soon as possible, it was already working well before 1.4.
-> Just take a video f.e. with your IPhone with 60 fps or faster, import it to your project, reduce the time speed to lets say 30 fps and then go to frame & fitting (or whatever its called in english) and add a mark at the beginning with size 1.100 and at the end of the clip with 1.000 and let the preview run.
EDIT: and this is for everything u want to do in slow mo. just try it with fade in/fade out of the blending or any other transitions. that really suxx