It will be mate exactly the same phone with exactly the same beta build. Many problems like that are fixed with a factory reset. If 1 person is suffering lag so would all of us as we are all on the same beta build. If 1 person is suffering lag and the rest of us are not time for them to do a factory reset. Bet they have never done a factory reset since they started beta hence why some people get issues like that. I always do a factory reset first to see if the problem goes before I report it. As standard you do a factory reset first if you encounter a issue. If it's still the same after a factory reset there is a problem with the rom. We would all have the same issue if it's a rom problem.