That cause by connection problem, Connection lags or whatever..it happens maybe cause they are doing something on the server or maybe your net is being use up by download or your net could have happened to slow down because the host of your internet are having some kind of issues.
Anyway as for a fix i suggest you go to speedtest and see if it's how fast your suppose to be going if not and it's lower then their your answer the only other reason that a client would lag is because something in the background is taking up ram space could be virus,background program,skype etc.
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