Lost proj source file

I have several projs saved and, when I re-open them, there are no source files or my inwork video in timeline at stage where I saved it. I used "save as" (to the default location) and opened that save. Fresh inst but, it has updated each module as I open them for a new version (2018 I assume). Is there something new in '18 that I'm missing? Very frustrating to put in several hours of work only to have it disappear the next day when I open the project file.

Thanks for any info/help with this one!