File has unexpected size (7660 != 7398). Mirror sync in progress?

getting this error when running system update

sudo apt-get update
Hit:1 http://us.archive.ubuntu.com/ubuntu focal InRelease
Hit:2 http://us.archive.ubuntu.com/ubuntu focal-updates InRelease                                                                                                               
Hit:3 http://us.archive.ubuntu.com/ubuntu focal-backports InRelease                                                                                                             
Hit:4 http://dl.google.com/linux/chrome/deb stable InRelease                                                                                                                    
Hit:5 https://download.docker.com/linux/ubuntu focal InRelease                                                                                                                  
Hit:6 http://us.archive.ubuntu.com/ubuntu focal-security InRelease                                                                                                              
Hit:7 https://download.sublimetext.com apt/dev/ InRelease                                                                                                                       
Hit:8 http://us.archive.ubuntu.com/ubuntu focal-proposed InRelease                                                                                                              
Get:9 https://brave-browser-apt-nightly.s3.brave.com stable InRelease [4,317 B]                                                                                                 
Hit:10 https://apt.releases.hashicorp.com focal InRelease                                                                                                                       
Hit:11 https://deb.opera.com/opera-developer stable InRelease                                                                      
Hit:12 https://packages.microsoft.com/repos/azure-cli focal InRelease                                        
Hit:13 https://packages.microsoft.com/repos/ms-teams stable InRelease                  
Hit:14 http://archive.canonical.com/ubuntu focal InRelease                            
Get:15 https://mega.nz/linux/MEGAsync/xUbuntu_20.04 ./ InRelease [2,441 B]
Get:16 https://brave-browser-apt-nightly.s3.brave.com stable/main amd64 Packages [7,398 B]
Err:16 https://brave-browser-apt-nightly.s3.brave.com stable/main amd64 Packages
  File has unexpected size (7660 != 7398). Mirror sync in progress? [IP: 99.84.126.35 443]
  Hashes of expected file:
   - Filesize:7398 [weak]
   - SHA512:8bd5e753fce431f6e7cf8111722cd89c296598b62b335fd839e4c85c90d348a61347a456f3f8d117e3ae4c035cff797549eb2f4d5ecdccbc949d397c1b7e56ca
   - SHA256:bb14d8a13aac904ca0410bf622f7d062f3336273d94a7a33b881d223234f7167
   - SHA1:fe3f258c595be080b276763c160a04c4bc2f59ca [weak]
   - MD5Sum:6a2fa07708eb6be197aae80b61a5906c [weak]
  Release file created at: Sat, 31 Jul 2021 06:46:39 +0000
Fetched 6,758 B in 2s (3,237 B/s)
Reading package lists... Done
E: Failed to fetch https://brave-browser-apt-nightly.s3.brave.com/dists/stable/main/binary-amd64/Packages.bz2  File has unexpected size (7660 != 7398). Mirror sync in progress? [IP: 99.84.126.35 443]
   Hashes of expected file:
    - Filesize:7398 [weak]
    - SHA512:8bd5e753fce431f6e7cf8111722cd89c296598b62b335fd839e4c85c90d348a61347a456f3f8d117e3ae4c035cff797549eb2f4d5ecdccbc949d397c1b7e56ca
    - SHA256:bb14d8a13aac904ca0410bf622f7d062f3336273d94a7a33b881d223234f7167
    - SHA1:fe3f258c595be080b276763c160a04c4bc2f59ca [weak]
    - MD5Sum:6a2fa07708eb6be197aae80b61a5906c [weak]
   Release file created at: Sat, 31 Jul 2021 06:46:39 +0000
E: Some index files failed to download. They have been ignored, or old ones used instead.

Solution 1:

Solution ... just wait several minutes and rerun the update

sudo apt-get update

evidently I ran the command in middle of system updates getting refreshed upstream ... personally system should not expose this level of detail to enduser ... certainly it should avoid printing out the word error instead make this a notice message