If you have a very big file that doesn't match the standards in video formats, then the software will load it, but a little slow since it has to process it. This ensures you will have a nice experience after it has been loaded completely.
Another cause is the integrity of the files you are trying to add. If your video is somehow damaged, then the software will have problems loading it.
As always, download the latest version of Filmora to avoid encountering any bugs or issues: https://filmora.wondershare.com/
