This project is invalid or corrupt and cannot be opened. It may have been created in an earlier version of Storyline problem

Blaming the user who's doing everything correctly is not an adequate response.

If your program is prone to these errors, you should either fix them or post prominent warnings as to the fragility of the project files created in Articulate Storyline and the necessity to take extra steps to preserve one's work -- in this case, saving religiously to Team Slides appears to help. 

I am suspecting that the cause in my case has to do with not updating the program as frequently as I might (I work on a network at work and I would have to write a ticket every time I get a notice that updates to Articulate are available and they would get back to me, maybe, within a few days).

Blaming the user doesn't get to the real problem.  I may have just lost another three days' work.