Why didn't the whey separate from the curds when I tried to make Shankgleesh cheese?
Yogurt is very sensitive and there are many possibilities here regarding why this recipe hasn't worked out, however the very main point that stands out for me is that you heated the yogurt to coagulate the protein. 

This is not how it is done in traditional shanklish making. The yogurt is poured into an elongated container and gets covered and put on the floor. Then you need to sit on the floor and shake the container from front to back. Every ten minutes or so stop, uncovers the container and skims the butter which has formed on top. Continue doing so, until half of the butter is removed and the yogurt has become low in fat (partially skimmed). At this point you should be able to use the skimmed yogurt (known as shenineh) to heat it up and separate the curds from its water and make the cheese.