I have the same issue. And called spectrum service representative and he said signal levels need to be adjusted and I am not sure what it is. He put a request to some other team and said some one will come adjust the signal levels for lines coming into the home and I don’t need to be available.
I am am not sure any one came and did anything. I still face the same issue some times Ondemand works and some times goes blank as you mentioned.
I have no confidence in spectrum. Service personnel. I stopped calling them