Don't heat it and stirr again - your one is ok. Shake it very well right before use. It's consistency depends much on the quality of potassium carbonate and sulfite. But it works fine anyway.

I'm making several liters per month of this paste, and eveyr time it is different if I take different carbonate. When the carbonate is very good, paste is a two tone liquid like yours, sometimes it is like a cream (this happens when I use potassium carbonate wich gives white precipitate when it is diluted in water).

But I found no difference in the development results of all this batches.