Lag during the game

Hi, I need an advice for Warcraft 3. After the 20th minute of playing DOTA every time when there’s a battle I have lag and more than 600 ping and I see only pictures till battle ends and after it the ping goes down again. I have checked my PC and everything seems good, my internet also is not an issue. So is there anyone who has the same issue, I would appreciate an advice. Thank you in advance