Corrupted Project - Invalid Clip Producer - Invalid Clip Removed

Can anyone shed some light on why a project I've been working on in the last week has suddenly corrupted with a message "Sorry - kdenlive" and a great long list of entries like this come up in a dialogue:

Invalid clip producer 52_4_audio etc etc

Invalid clip removed from track 4 at 2,572 etc etc

I've has so much hassle with sunab PPA 'unstable' builds in the last couple of weeks with crashing, then render dialogue failing to appear causing crashes, both of which did not happen with daily build script builds, which I ended up using in preference, now this project above with many many cuts if foobar, next to nothing left on the timeline.

I've gone back through old builds, project back up files and all say the same.

Not complaining, corruption is just one of the risks of using 'unstable' builds of coarse, just wonder before I start the project again if there's a solution or work around.

***EDIT***

I've managed to salvage a project back up also manually compared and edited the kdenlive xml project file so ok for now, still interested to know possible reasons why corruption happened.