[NetworkDispatcher exception io.netty.handler.timeout.ReadTimeoutException]

I cannot upload a .log or .txt an error message comes up saying -200.

How should I upload the files now?

[NetworkDispatcher exception io.netty.handler.timeout.ReadTimeoutException]

Hello,

My friend has a problem with our minecraft server.
My friend gets kicked out after a few seconds-minutes after he joins the server.
However, I and other players don't have the problem.
Maybe it's because his internet is via Vodafone.
I then looked into the console and found an error before my friend was kicked out:

NetworkDispatcher exception
io.netty.handler.timeout.ReadTimeoutException