I have been using LR for several years now, on a CC subscription so I have the latest update. I have encountered what seems to be an issue when I am applying bulk changes via Develop/ Copy then Paste. This centres around using large numbers of photos for timelapses, currently 400 max. When I apply the changes, it seems that the changes are not applied evenly across the whole range , unless I slowly scroll the thumbnails filmstrip across the screen. There will be 3 dots on the top RHS of each thumbnail, and these disappear as the changes are visibly applied. If I leave it for a while, then Export using the template out of slideshow, there can be visible flickering in the finished article, particularly evident if have have applied Crop. If I go back to the filmstrip, and scroll across, I will find patches of thumbnails which appear not to have the changes applied. It almost seems as though the Develop changes cannot be applied unless the thumbnail is visible on the filmstrip. So, scrolling across slowly, letting the changes be visibly applied, across the whole batch, then re-exporting, cures the issue.
This is a separate issue from exposure flicker during day/night timelapses--I am aware of this, and am currently trialling LRTimelapse for this reason, results have been good.
Are you also applying Autotone to these batches?
Not knowingly, ie, if it is not a default preset, I am not doing it.
Similar symptoms have been reported for applying autotone and lens profile corrections to large batches. E.g see Lightroom: Applying Auto Tone to a batch of photos loses subsequent develop settings | Photoshop Family Customer Communi…
Can you post a screenshot of the Develop Settings > Copy Settings window, so we can see precisely which settings are being copied?
You could try this workaround: After copying the settings, select all the photos, and do Library > Previews > Build Standard-Sized Previews. At least with the autotone and lens profile corrections bugs, this forces LR to actually apply the develop settings.