Have had to reflash CM 11 on my Nook HD+ several times
CM is a very interesting mod. I have had the same issues. One of the options you can try is when it gets laggy is to change the theme from the Hex to the Holo (android default) and it can help with the lag and lack of response. 

That is what I did and I have not had issues. 

Source: My OnePlus One and my past