There are many possible reasons why PD doesn't work with these clips. Since we don't have any information about your system or the clips themselves, it would be helpful to see a sample clip to at least see how it's encoded.
You can't attach any video clips larger than 5MB in the forum, so you'll have to upload it to a cloud service like Google Drive or OneDrive and then post a shareable link here. Please see the
Share a file publicly section in this Google
FAQ or this OneDrive
support
page if needed.
You can also try transcoding the clip in a free app like Handbrake into a more compatible format, but again it would help to have an actual clip to work with.