Maybe, when you upgrade to 5.1.4 is should works
Was there a bug with 5.1.2 regarding this?
This seems very unlikely that simply adding a static ID is the root cause of the problem. In just about every IG region I create I give it a static id. Almost every IG in the Sample IG app and the IG cookbook app has a static id.
It says the element is not found. Does it exist? Look at the page source to see what may be wrong. Try $("#emp-members-region")
Why are you using jQuery Migrate?
Run the page in debug mode to get a better stack trace with line numbers in uncompressed code.
Create a reproducing case on apex.oracle.com if you want someone to take a look.
Is the static id unique and a valid id?