When you are on a boat and you leave it you appear far away from that boat.
If you disconnect and reconnect you also appear on that place. Is like if the server shows you like if you moved on one velocity but you are actually moving on another one, slower than what you think.
Linked issues
duplicates
Comments
CubeTheThird
Duplicate of MC-2931 - If you have not, please use the search function in the future, to see if your bug has already been submitted. If you could not find the original report, please comment with the keywords you searched for.