The cam lobes make "hills" that push the sprocket "downhill", so under slow rotation, the cam may counter-rotate, giving the slack where you note it. That is not a definite indication of jumping time, or having a bent valve. Make sure you are rotating the engine the right direction. Rotating the wrong way can put excess slack on the untensioned side and the belt can jump, and you may well bend a valve. I'm not up on that engine, but it may have a hydraulic belt/chain tensioner that is not under pressure unless the engine has oil pressure, and/or the tensioner spring may be dying. Hand rotate the engine slowly and gently in the correct direction (so the cam sprocket pulls on the untensioned side of the chain/belt) through two complete revolutions of the crank (one revolution of the cam sprockets) to see if there's any valve interference. A bent valve may not show up in this test. Then rent a radiator tester and see if the head gasket is leaking. Then take the head off and see what the problem really is...

The Gates website shows all the engines are interference engines, but that's only for the rubber band engines. If you have a chain, it's not on that list.