I had to upgrade to 16GB of ram to alleviate the problem you had. Some effects are really taxing like particles or blurs. Also manipulating embedded large files like photoshop, AI, and pre-rendered videos can slow it down. So if you don’t have enough Ram, your system will hang, and will interrupt the render.
Simply designs 8GB will work, but once you get into more complex effects and compositions, or start using 3rd party plug-ins, you will need 16GB minimum.