Zipping to transfer files between PC and Mac breaks Lightroom's ability to detect Smart Previews

[CoryG-L]

Issue: 

• Lightroom Classic Version Number: 10.4
• OS Version Number: PC - Windows 10 Pro / Mac OS Catalina - 10.15.7
• This issue involves a workflow with computers that are not physically connected, starting on PC and finishing on a Mac
• The original files being imported to the PC catalog are on NAS. We only wish to work with Smart Previews on the Mac, and then ultimately plan to move the finalized .lrcat file back to the PC, to export using the original files at the end of this process

Steps to reproduce:

1.  Create a new catalog on the PC
2.  Import desired images (For our purposes, 2834)
3.  Build Smart Previews for all images
4.  Locate the system folder location containing the .lrcat and Smart Previews.lrdata 
5.  Select the .lrcat and Smart Previews.lrdata folders, zip them together
6.  Upload the resulting zip file to any cloud storage service
7.  Download the zip file from your Mac, unzip it
8.  Open the .lrcat file on the Mac

Expected result: 

The Smart Previews which were created and packaged should be recognized by Lightroom, by virtue of the fact that we made no alterations to either the Smart Preview folder name or its location relative to the .lrcat file. We simply zipped and unzipped them. This process works flawlessly when working PC to PC.
Actual result: 

On a Mac, Lightroom cannot recognize that the Smart Previews exist. They all are present on the system in the exact same relative location as we would expect- the exact quantity are there, they have unchanged filenames, folder names all preserved, etc., however Lightroom will not detect the existing Smart Previews. We can enter the folder structure via Finder on the Mac and verify that every single image is there as we would expect, but Lightroom will not detect them.

After multiple tests and searches through anecdotal user forum reports over the years, I can say with almost absolute certainty that it is the zipping step causing this issue. Something about the act of zipping these files is breaking the expected file path/relationship that Lightroom is looking for when opening the catalog file on the Mac.

Adobe support has suggested that we move the files from PC to Mac without ever zipping them in between. In a scenario where physical proximity between the two machines is not possible due to distance, thus preventing such a process from occuring simply by using external hard drives, the only option here seems to be to employ a third-party cloud storage service as a rather complicated workaround for this simple need.

We seem to be forced to use a cloud storage desktop app, to upload all the folders and subfolders containing Smart Previews (not zipped), and then run a selective sync process from the Mac app to obtain the files contained in only those Smart Preview subfolders, without ever having zipped them along the way.

[JohanElzenga]

On a Mac, the smart previews folder is a package. That may be the problem. See here how to change an ordinary folder into a package: https://discussions.apple.com/thread/2586142

[CoryG-L]

Johan, thanks but that's not the issue. The Smart Previews folder is correctly being recognized as a Package on the Mac system already. Lightroom simply cannot do the next step of reading any of the Smart Previews contained within, and displaying them within the catalog to which they should be related

[Earth Oliver]

which zip utility are you using? have you tried other compression formats like .rar?

[CoryG-L]

The issue persists when using both the default Windows compression to create a zip file, as well as with WinRAR and a rar file.