Lightroom Classic 15.6 intermittently “Not Responding” building Smart Previews from SMB/NAS, same files work locally

I am seeing reproducible UI hangs in Lightroom Classic 15.6 when building Smart Previews from photos stored on a Synology NAS over SMB.

System

• Lightroom Classic 15.6, build 202609251514-f839cde9
• Windows 11 Pro 26H2, build 26300
• Dell XPS 13 7390
• 16 GB RAM
• Intel UHD Graphics, driver 31.0.101.2130
• Lightroom GPU preference: Auto
• GPU for Preview Generation: Auto
• Lightroom catalogue is stored on the laptop’s internal SSD, not on the NAS

The relevant System Info is attached.

Problem

When I build Smart Previews for photographs whose originals are stored on my NAS, Lightroom intermittently enters a Windows “Not Responding” state.

It normally recovers by itself and the Smart Preview generation continues in the background. When the UI becomes responsive again, the preview counter has advanced, so the background task appears to continue while Lightroom’s interface is blocked.

The behaviour is significantly better when the exact same source photographs are stored on the internal SSD.

Controlled test

I tested the same set of 20 photographs.

Test 1, originals on NAS over SMB:

• 20 Smart Previews took approximately 1 minute 30 seconds
• Lightroom briefly entered “Not Responding” during generation
• The preview-generation counter continued progressing while the UI was unresponsive

Test 2, exact same 20 files copied to the laptop’s internal SSD:

• Created a new temporary Lightroom catalogue
• Imported the same 20 files from the SSD
• 20 Smart Previews took approximately 1 minute 10 seconds
• Lightroom became slightly laggy occasionally, but never entered “Not Responding”

This suggests that the UI blocking is associated with generating Smart Previews from network/SMB storage rather than simply the CPU load of generating Smart Previews.

Preview cache testing

I also tested the preview databases to rule out a damaged cache.

I closed Lightroom and moved both:

Previews.lrdata

and

Smart Previews.lrdata

out of the catalogue directory so Lightroom had to create completely fresh versions.

With a fresh normal preview cache, Standard Previews currently build at approximately 4 seconds per photo and Lightroom behaves reasonably normally.

With a completely fresh Smart Preview cache, starting Smart Preview generation still caused Lightroom to become unresponsive. Therefore the behaviour does not appear to be caused by corruption of the existing Smart Preview database.

I also previously created a completely new temporary catalogue while leaving the source photographs on the NAS. Lightroom still showed substantially slower folder/file access, so the issue does not appear to be specific to my main catalogue.

Catalogue checks already performed

• Optimised the main Lightroom catalogue
• Restarted Lightroom and Windows
• Tested with a new catalogue
• Recreated the normal Preview cache
• Recreated the Smart Preview cache
• Restarted the laptop, router and NAS

Network checks

I also investigated the NAS/network connection because I wanted to rule out a basic network bandwidth problem.

NAS: Synology DS418
NAS Ethernet connection: 1 Gbps
SMB dialect: 3.1.1
Laptop connected over 5 GHz Wi-Fi
Wi-Fi negotiated rate approximately 866.7 Mbps receive / 780 Mbps transmit
Wi-Fi signal approximately 89%, RSSI approximately -49 dBm

Large sequential transfer tests currently give approximately:

• SMB file copy: ~50 MB/s
• Synology File Station/browser download: ~60–70 MB/s

Ping test to the NAS

• 116 packets sent
• 116 received
• 0% packet loss
• minimum 1 ms
• maximum 48 ms
• average 5 ms

So there appears to be adequate throughput and no packet loss. The issue is specifically more noticeable during Lightroom operations involving network-hosted originals, particularly Smart Preview generation.

Additional observation

Standard Preview generation is now substantially better than it initially was and is approximately 4 seconds per photo. Smart Preview generation is the operation that most consistently causes Lightroom’s UI to enter “Not Responding”.

I understand that an older integrated GPU and network storage will make preview generation slower than a modern desktop using local storage. However, the key difference is that the same 20 files on the internal SSD make Lightroom slightly laggy but do not produce a Windows “Not Responding” state, while the NAS-hosted versions do.

Is this a known issue/regression in Lightroom Classic 15.6 involving Smart Preview generation from SMB/network storage?

I can perform additional controlled tests if needed.

I found an existing Adobe Community thread concerning Lightroom freezes during preview generation. Although the original report concerns an older Lightroom version on macOS, a user running Lightroom Classic 15.6 recently reported that previews fail for files on an external volume while files on an internal volume do not show the same problem. My issue may be related, but I have opened a separate report because my reproducible case specifically involves Windows 11, SMB/NAS storage and Smart Preview generation. 
Possibly related Adobe Community thread: