P: Scan For Metadata Updates causes spurious metadata conflicts

[johnrellis]

Synchronize Folder > Scan For Metadata Updates can cause frequent spurious metadata conflicts for TIFFs that are stored on NAS. 

Over the years many people have reported spurious metadata conflicts that Adobe hasn't been able to track down, and many of those reports involve photos stored on NAS.  Here's a recent report:

https://feedback.photoshop.com/photoshop_family/topics/before_after_comparison_of_metadata_conflicts...

While the particular use case here may not be that common, it may provide a reproducible test case that points to the bug (likely a race condition) underlying all those other persistent reports.

Here are the steps that consistently produce the spurious conflicts in my configuration:

1. Connect to a network volume on a 2013 iMac running MacOS 10.14.6. The volume is mounted with SMB 3.0.2.  

2. Place 4 1800 x 1200 TIFFs (about 13 MB each) in a folder on the network volume.

3. Import them with Add into a LR 9.0 catalog running on a 2019 Macbook Pro running Mac OS 10.14.6.

4. Select all 4 photos.

5. Do Metadata > Save Metadata To File.

6. Do Synchronize Folder with just Scan For Metadata Updates selected.

7. In the Metadata panel, change Caption to "a" (changing all 4 selected photos).  Often, one or more of the photos are marked "Metadata has conflict".

8. Repeat steps 5 - 7, changing the caption to "b", then "c", etc.  Observe the metadata conflicts that appear randomly on the photos.

Here are screen recordings showing this bug, with two different TIFFs:

https://www.dropbox.com/s/e78s6fudehcls95/sync-folder-spurious-2.2019.11.21.mov?dl=0
https://www.dropbox.com/s/9sz4nz3t3pmk2hc/sync-folder-spurious.2019.11.21.mov?dl=0

[SatishT]

John,
Thanks for steps, we will try to reproduce this issue and let you know if we need any further information.

[johnrellis]

Some more notes:

- Here are the photos shown in the videos:
https://www.dropbox.com/s/nsbtwasbydbs1qw/sync-folder-spurious.zip?dl=0 

- The client machine was connected to the server via Google Wifi, pretty fast Wifi but not as low-latency and fast as ethernet. The higher latency may be more likely to provoke the supposed race condition.

- The iMac server, though plenty fast as a desktop, wasn't a speed daemon for NAS (likely due more to MacOS than the hardware).  It's mild sluggishness as NAS perhaps may be more likely to provoke the supposed race condition than a faster dedicated NAS.

So to replice this issue, I recommend using an older desktop with rotating disk storage, using SMB over Wifi.