A weird bug that seems to "reset" your player.

So I've been getting this bug twice now and man it's a bad one. So the bug is that once you log into a server you can sometimes lose all your stuff and your player will kind of reset. So you'll spawn at the worldspawn point. This is VERY enoying as I just spent 3 hours straigt playing around with enchantment commands. And I made an overpowerd armor gear and weapons too. And I went in a singelplayer world because I hade a command there that I wanted to copy so I did that and when I went back into my server my player got reset. At first I did not care because I knew that I made a copy of the armor parts and put them in a ender chest. But it was all gone there too. This is by far the worst thing that have ever happend to me in Minecraft. Is there a fix? If not, I would reccomend you start to work on one.