First, check what version you are logging onto the server with. If it is below 1.8, then try connecting with a version above 1.8. If it is 1.13, try connecting with 1.12 to see if that fixes the issue. If that does not work, try connecting to creative.mcpz.net instead of play.mcpz.net (and doing /hub if you need to get to other gamemodes). If that still doesn't work, check your internet connection. You may want to restart your router as well. If none of that works, you may want to restart your entire game or redownload minecraft. If that still doesn't work, private message me on the forums and I can help you out further.