Owners/service Manual problems of the 2012 Honda Civic

My car (manual) was parked in first gear on an incline in my jobsite parking lot. The emergency brake was not engaged. Within 1-2hrs it rolled back nearly hitting my place of business and an ac unit. It is all on camera. It rolled some, then stopped, then again rolled and stopped. It has never done this in the past but I typically have the e-brake engaged. Days before, I was sitting in my same vehicle after it was parked for several minutes and it jerked suddenly. It did not roll back at this time.