Just to rule out a likely issue, are there any external, or networked HDD's on your system?
The Rendering and the resultant files are linked in the PrE Project File (PREL), and those links are absolute Paths, so if they cannot be accessed, then there will be an issue.
Thank You for respond.
I have two internal HDD in my system. All project and scratch files are on OS system drive
while media ( video clips , photos , etc) are on the 2-nd HDD.
Thank you for that info. That eliminates a common problem.
Other than the location of the Project files' location (I'd set those up on the second HDD, where your media files are located, to free up I/O processes from those of the OS and program), I do not see a reason for the loss of the Render Files' links.
In the Scratch Disks for your Project, there should be a Media Cache folder, with the Render files. Navigate to that, and check that you do have Render files. They will have rather abstract numerical names, but should be in the sub-folder.
Good luck, and please let us know if those Render files do exist.
Strange thing , all scratch disk in preferences for version 9 are set up
"same as project". There is Media Cache folder ,but nothing inside,
this folder is empty.
I have same/similar problem.
In my case the still images have stayed rendered but all the video clips have gone red