apt-get error in local repository

We have created an offline Ubuntu 20.04 repository using apt-mirror as per the directions given in https://www.linuxtechi.com/setup-local-apt-repository-server-ubuntu/

In a few local machines we were able to install packages using apt from the offline repository. But in some other machines, while using the command "sudo apt-get update", it is giving an error "File has unexpected size (1536 != 1260)". Please refer to the following image. It seems like an error related to cnf. We found that the file in the repository has a size 1536. We checked Internet and found that the file has size 1536 only.

How to solve this issue? We are also wondering why the same issue is not reported in other machines? (All machines have Ubuntu 20.04.3)