Always, always, always try to be as detailed as possible when making such reports.
Which "LPMA" you are referring to ? Default 3rd party ? If it's 3rd party, it's a Marketplace airport ? Which gate you used ?
The pushback truck had no sooner stated moving and it dissapeared causing the aircraft to violently twist form side to side and bounce onto the tarmac.
Maybe it was the *scenery* that had an "hole" in the Terrain, causing the Pushback truck to fall, which in turn caused the airplane to bump as well. That's why it's important to know exactly which scenery and which exact location this happened.
The GSX Pushback MUST follow the terrain, otherwise it wouldn't be able to support sloped airports. Which also means, if there's an hole in the terrain, it will fall through it.