Video thumbnails are not updating in trimmer'view

[rameez7878]

I have added following code for trimmer in viewWillAppear:

videoRangeSlider.delegate = self
videoRangeSlider.setVideoURL(videoURL: url)
videoRangeSlider.minSpace = 0.0
videoRangeSlider.maxSpace = 20.0
videoRangeSlider.setStartPosition(seconds: 0.0)
videoRangeSlider.setEndPosition(seconds: 20.0)

When i comes to trimmer screen first time then this code updates the video thumbnail in trimmer's view. Then i move to the next screen for further advance video editing. After advance editing i do update my URL of video. Then if i navigate back to trimmer screen, video thumbnails are not updating. Sometimes thumbnails are updating and sometimes not.