When i try to sustain a key and then press a couple of notes the sustain is gone and i dont know to fix it.

That's not much to go on. Are you using the sustain pedal to sustain the first key? And you then pressing more keys while you are still holding the pedal down?

Please provide more detail about the performance and parts and the sequence of things you are doing.

The SIMPLER the example the better.

I think it might be issues with the sound engine polyphony ive read another forum on this website and it works

If you layer 8 sounds and many of those layers are drawbar organs then you're going to chew through polyphony quickly.  I say drawbar organs because they tend to use all elements in a Part.  That's 8 units of polyphony per key pressed.  Multiply that by number of Parts (and average the element consumption for the lot) then multiply by the amount of fingers you mash down at one time.  Then multiply by the number of new notes you add with the sustain pedal engaged.

You can certainly construct a "bad" Performance that is expensive in terms of resources.  There's always a way not to do that expensive stuff and still achieve a similar result.