It wasn't evident that your initial post had any tie-in to polyphony - but your latest description is moving in the right direction.

You should detail how to construct your Performance that's problematic. What preset do you start with (some piano, I'm assuming)? What specific other Performances do you merge in? Detail which PART has which sounds.

Also detail which sounds need to be heard simultaneously and which are mutually exclusive. There's a difference between needing, for example, Piano+Strings at the same time or Piano always alone at some times then strings alone at other times.

If you choose "CFX + FM EP" as your piano, then rotating the Super Knob clockwise will change the piano to an FM-X electric piano. FM-X is a second engine (second to AWM2 - the sampling engine) which has its own pool of notes for polyphony. If you're running out of notes - this could explain why rotating Super Knob clockwise helps you hear the the piano. This doesn't necessarily help the problem - but could explain the "why" of what you're experiencing in terms of Super Knob helping.

Specific names of the sounds is important since some may be more taxing on polyphony than others. There may be a better way to manage the sounds you're trying to combine.

So it’s a case where, for example, I select a sine lead from the synth lead category, it plays and drops some keys from time to time but if I should select another lead, I get no sound at all not even if I turn up the super knob. Majority of the categories eg., Keyboard, Synth/Pad, Strings etc. I’m not getting any sound from any of the categories listed. What could possibly be the problem?

If the category of the sound does not match your selection, it is likely you are mistaken about the context. Sounds like it could be just a newbie, “I’m lost” issue.
But without a better description it’s very difficult to know what you might be missing.

If you truly think you’ve read the manual and this is just incorrect behavior, please contact the store where you purchased it, they may have enough experience with the instrument to point you in the right direction, or replace the instrument if it turns out to be a real problem and not just an “I’m lost” issue.