On the Mc sever, there is a bug. Kris reported a missing chunk. can someone help us?

It's problem a problem with minecraft, not the server. A server is a place where many players can't play together, those missing chunks are bugs with the code on Minecraft.
There's a way to fix that, go on the Minecraft Installer, and click "repair", it will repair all the errors, etc.
It might work.