NFS mount disconnecting after a few minutes

Hello,

on Big Sur version 11.4 I am using a VM and mounted as NFS:

sudo mount -t nfs -o resvport,locallocks,rsize=32768,wsize=32768 <mount_point>

Usually, after a few minutes (5-10) of using the VM, from terminal or finder or any text editor, I get a disconnected error message,

The SSH connection in a terminal (ssh <USER>) ends with a message: `client_loop: send disconnect: Broken pipe`.

If I remember correctly, before updating the macOS to version 11.4 I had version 11.3 - where I had the same VM running without any disconnection.

Any idea what options to add or actions to take?

Thanks,

Laszlo