Could be any number of things. The barrel is actually nothing more than a rifled metal tube inside a completely synthetic 1 piece shroud and breech block which you'd have to bend to make the inner barrel bend and just knocking it over shouldn't do that.
Check the stock screws aren't working loose, barrel pivot screw same thing, crud in the barrel wedge not letting it lock up, check the breech seal since it's not unheard of to get a bad one in a Hatsan. You might also check that pic rail since it's a wrap around sleeve held by the end cap pin at the rear and a small grub screw on top of it near the front. Might well be loose and just need tightened down again.