what happened to the network?(from a noob)

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From the captures you have provided I don't see any serious problem.

FIN, ACK and RST

This is quite usual way to stop TCP connection. Can be observed very often.

Dup ACKs, out-of-orders

This is TCP built-in mechanism for handling lost and reordered packets. In your case it seems there are regular out-of-order packets coming to receiver. Although the consistent pattern is interesting, this is nothing TCP couldn't take care of, and in this case the influence of reordering is unnoticeable.

From materials I learned before, they are very serious problems. Am I right?

It depends. They could be or could be not (as it is in your traces).