Hello, How are you?

I have a rather curious problem.
In a game on a server, all the players except me, who is the administrator, have a problem with a couple of chuncks. They cannot build, break, chop, open doors or chests, or interact with any items between these chunck. They can only walk. It's like a kind of corrupt zone. At first they could but a time has come when they cannot do anything within those limits. Any ideas? The truth escapes me.

PS: I can do everything included in survival mode, I don't need to be in creative