Why would a lower network band browse faster than the higher band?

[Kross]

For one of my internet service providers, when it is at 4G, the browsing network becomes dull. But when you switch it to 3G, it becomes very fast.

How can it be explained that browsing with a higher band is significantly slower than with a higher band?

 

[eLdavis]

I think maybe because a lot of persons are using 4G at that particular time hence the network speed becomes slower.