Where does id come from in the HAVING? Please qualify it.
The HAVING maybe should be WHERE? Or ON?
Some of these composite indexes may help:
assignment: INDEX(Project_ID, assgin_name)
hub_coordinator: INDEX(Employee_ID, Assign_ID)
hub_coordinator: INDEX(Assign_ID, Employee_ID)
You can use this portable version of workbench 5.2.47 CE for connections to MySQL server 5.xx and the installed version 8 for newer versions of MySQL Server.
Although I use this software with no problems until now, this is not from my authorship, use it at your own risk.