Unstable Ping in Random Maps

I have come across an issue which only started once I got to mapping. I will sometimes enter a random map instance which causes massive lag spikes, it feels as though everything is majorly slowed down and it seems to get worse with a higher mob density. Once all the mobs are cleared then things speed up intermittently. This issue only seems to occur within that specific map instance and nowhere else in the game so once I enter my hideout then the lag spikes are gone. I have tried things like removing all MTX but nothing has helped so far. In most maps my ping is otherwise stable. I play on the South African realm with an average of 40ms ping. I am playing an Ice Nova of Frostbolts build.