8.0 code has much higher RAM requirements than 7.7.x. Please consult the sizing guide and make sure you have enough memory to run Visual RF for the amount of devices being managed and the # of floor plans you have.
Also, HTML5 mode for Vis RF seems to take up much more CPU/RAM so resources are going to be important.
I converted from 7.7.10 to 8.0.1 and things got really sluggish. I only had 16GB RAM for 1500 devices under management and had to increase to 32GB RAM to get performance back. Suggested RAM for that many devices however is 48GB which is quite a jump!