Upon joining a server from a main server it says "Disconnected from server."

When I'm in a main server like FallenTech and I try to go into their other little servers like prison and skyblock most of the times my screen gliches then Minecraft says, "Disconnected from server." Once and a while I would be able to get in the server but most of the time no. I would this fixed so I can join servers with ease. I love this game but it does have its flaws once and a while. Thank you for reading this and have a nice day.