The project in question IS the iterative save meant to protect against this exact type of failure.
My concern is not knowing what precipitated the corruption, particularly given that the project file was behaving as expected the last time it was opened - what happened during that intervening period in which the project was not accessed that it became corrupted? or, did the project file become corrupted as a result of the save operation when the project was last closed.
I have noticed that Substance Painter will sometimes crash, hang, or stall out when Substance Painter windows are moved between monitors in a dual monitor display - perhaps that is related.