Video Slideshow not working in LrC 9.4 above some limit on number of images

[ItWasNotMe]

Lightroom Classic 9.4 Camera Raw 12.4

macOs 10.13.6 - all latest patches applied

I'm trying to create a 1080p video slideshow from 427 images - it repeatedly fails

• The process runs for a very long time, showing periodic peaks in CPU usage
• It then stalls running at 1 or 2 % of the CPU
• Using the Activity Monitor I can see that it has opened every image (and according to the monitor still has them open)
• It has then opened many, but not all of the images again (both times I tried, it gets to the same spot about 2/3 of the way through)
• By that point its showing as using c91GB, yes thats GB, of virtual memory
• It does not get to the point where it runs amecommand to do the rendering so has not started to produce the .mp4 file

Throoughout this process (which takes many hours) the application does not respond and when active the cursor is the infamous 'spinning beachball'

There is nothing 'wrong' with the images - I can successfully create a pdf slideshow using exactly the same collection. NB All the images are multi-layer tiff files produced by Photoshop by round-tripping from Lightroom Raw files.

I can create 1080p slideshows from smaller selection of the same images (e.g. first 257 no problem).

[ItWasNotMe]

I'm pretty sure its the number of files LrC has open:

• I used Lightroom to create jpgs from the images
• Placed these in a new Catalog
• Re-created the collection with 427 images (jpg now, not tif)
• Tried to export a 1080p slideshow

As expected, the initial CPU profile is different; but when it drops back to around 1% then the list of open files shown by the activity monitor ends at exactly the same place (except of course the image is now a jpg not a tif); about 2/3 of the way through opening the images a second time.

[ItWasNotMe]

For those not users of a Mac; it has an Activity Monitor - similar to Windows Task Manager. Using this you can see which files an application currently has open. This is a fragment for Lightroom whilst it's building preview images. I\ve topped and tailed it.

---------

37
/Volumes/Photomedia2/Lightroom Catalogs/MyPhotos/Lightroom Catalog Previews.lrdata/previews.db-journal
38
/Volumes/Photomedia2/Lightroom Catalogs/MyPhotos/Lightroom Catalog Previews.lrdata/root-pixels.db-journal
39
/Volumes/PhotoMedia/Pictures/1997/05 13 - Stourhead/022 - Stourhead - Pantheon - Interior.nef
41
adbe.dva.lr6.2
--------

I've run seversl slideshows that failed to complete. All show the same behaviour

1. Every image in the slideshow is opened - to be expected
2. According to the Activity Monitor, the images are not closed - so given a large enough slideshow Lightroom will eventully exhaust some resource
3. Despite already being open, the images are then opened again !
4. Sure enough a resource limit is reached

In the above example, you can see 37, 38, ..., 41. When this reaches 799 Lightroom effectively stops processing. It exhausts the resource, can't open any more files and so cannot complete the slideshow. Does not throw an error, just sits there consuming 1% to 2% of the CPU until the end of time