>>87259729" Every game world runs off of a game stage, a background number that affects what's happening. The higher this game stage, the better loot you find and also the stronger the zombies become.
This number gradually increases over time as you gain experience and grow in levels, but it also has multipliers based on the difficulty you selected and, you guessed it, your XP gain factor. Doubling your XP also doubles your game stage, so you're going to get tough zombies way earlier than you can even prepare for, and trying to power level only makes it worse since it only raises your game stage faster (extra faster now that it's doubled).
The only way to curb your game stage is to lower your selected difficulty, lower the XP gain, or just die a lot. The game factors deaths into your game stage and will naturally lower it if it sees you're having a tough time."
tldr: they gonna be fine