Games lag when something new renders?

In various games, I always have to load everything first before I can play lag-free. E.g.: if I want to go around in circles in the waiting lobby in Fortnite, it is very laggy. But once I've looked at everything, I can play fluently. The same in Minecraft: if a lot of new chunks are generated, I get short still images.

Specs: GTX 1660 Super and AMD Ryzen 5 2600

(Should be enough for the games, I think.)

Does anyone know a fix against it?

How much ram do you have

2 times 8 gb