I have no idea what might have happened but I can't imagine that PD15 had any role.

I say that because when clips are added to the media library and/or placed directly on the timeline, PD doesn't actually import or change them in any way. The project (PDS) file simply "points" to where each clip is located and then records the various editing steps to be applied to each clip when previewing or producing the project.

No source clips are ever included in a PDS file, and the only two ways to ever directly impact the actual clips in a project by using PD are to 1) manually choose Delete from disk by right clicking on a clip (or a selection of clips) in the Media Library; and 2) use one of the Pack Project Materials options from the File menu which will copy all project clips to the specified packed folder.

That's it. Nothing else PD does should impact any of the actual clips, even if a PDS file became corrupted or was deleted.

The fact that your backup has 28 clips implies that it might have been made during the time that the hundreds of clips were being deleted, or at least that whatever was happening didn't take everything in one fell swoop.

PD does have a function to delete temporary files after a default of 30 days. Those temporary files are stored in the hidden ShadowEditFiles, Preview Cache Files and PDRMUSIC.TMP folders which are created automatically on the drive set as the Export Folder in the current project. Is there any chance you'd manually moved any of your source clips to one of those hidden folders?

Thanks, Optodata, for your etailed answer.

What you comment was my initial guess, that's why I tried to discard first other possible causes (virus, windows,...).
Only after discarting those I decided to post it here.
The strange is that this never happened with any other applocation or by any other circumstances.
It only happened twice and under the exact same circumstances - working with PD15 in the middle of a project. And the only affected files are the ones only used for the project.

I will check as per your last suggestion (temp. files), but honestly not much hope.

I also checked for similar reported by users issues with PD and found something similar posted previously by other user indicating ".avi" files disappearing after closing and re-opening a PD project. Remains opened.

So, unless someone's able to bring something new, remains a mystery...

Thank you,
Vladimir

Quote I have no idea what might have happened but I can't imagine that PD15 had any role.

I say that because when clips are added to the media library and/or placed directly on the timeline, PD doesn't actually import or change them in any way. The project (PDS) file simply "points" to where each clip is located and then records the various editing steps to be applied to each clip when previewing or producing the project.

No source clips are ever included in a PDS file, and the only two ways to ever directly impact the actual clips in a project by using PD are to 1) manually choose Delete from disk by right clicking on a clip (or a selection of clips) in the Media Library; and 2) use one of the Pack Project Materials options from the File menu which will copy all project clips to the specified packed folder.

That's it. Nothing else PD does should impact any of the actual clips, even if a PDS file became corrupted or was deleted.

The fact that your backup has 28 clips implies that it might have been made during the time that the hundreds of clips were being deleted, or at least that whatever was happening didn't take everything in one fell swoop.

PD does have a function to delete temporary files after a default of 30 days. Those temporary files are stored in the hidden ShadowEditFiles, Preview Cache Files and PDRMUSIC.TMP folders which are created automatically on the drive set as the Export Folder in the current project. Is there any chance you'd manually moved any of your source clips to one of those hidden folders?

Quote Checked with EaseUS data recovery and could see/recover the FOLDER, but containing only 28 photos, instead of more than 400 different photos and videos.

I'm afraid I can't help with your main problem as to why the folder disappeared but I may be able to explain why so many files in the recovered folder were missing. You may be aware that when files are deleted they are not physically erased. They are simply removed from the directory and the space they occupy is marked as available for re-use. I think Windows runs a disk defragmenter in the background whenever it's booted up and this may have overwritten some of this space.

That's just my guess. Maybe someone with more expertise with Windows can confirm or deny this.

My hard disk is 0% fragmented right now because Windows 10 enables the defragmenter by default unless one changes it. Select delete from disk from the PD15 library does exactly that. The defragmenter becomes active only after a number of files are deleted on my system.