Initially purge the cache then Open LR, go to preferences -file handling and increase cache to 20 GB.
Restart Lightroom and then check again.
Thanks for getting back to me Rohit.
I had my cache set at 30 GB already but clearing cache and restarting helped for awhile yet did not resolve the problem.
I downloaded 250 raw files today and as usual synched them to a preset that includes tone curve clarity vibrance, chromatic aberration and so on.
I then went through them all to fine tune exposure white and black point etc.
I usually adjust the exposure, contrast, white and black points etc, then synch the next 10 or so images to that setting.
I proceed that way with no problems until about half way through the batch of 250 then Sync. stopped working.
Instead of emptying the cache again I tried "optimise catalogue" and that got the Sync. working long enough for me to finish the remaining files.
I'll be glad if this work around can repair the problem but it's disappointing that what used to be a reliable function (for me LR-4 and 5) can no longer be depended on.
Thanks again for your suggestions.
It seems to be working fine for me over more than 300 images, i am using Windows 10.
Indeed optimizing the catalog and checking the integrity of the catalog can do the trick for you.
While holding down the alt(Windows)/Option(mac) key open Lightroom, you will see a box appearing, click on Test integrity of this catalog, and then click on open.
I did as you suggested and used the Test integrity screen and LR opened up as usual, no notifications of any kind. I imagine that's good.
I've just remembered that I have my LR catalogue on my computer hard drive and my images on and external hard drive, would that have something to do with it do you think?
I think I'll move the catalogue over to be with the images and see...
This kind of file structure should not cause any issues, however i doubt if there is any kind of permission issues.
Would suggest you to keep using LR and if in any case you come across the same issue, move the catalog on external drive and check again, and keep us posted.
Will do, thanks.
After no such problem most of my Lightroom history, I'm now getting this as well in 2015.4 Mac. And, selecting a bunch of images in Library mode and clicking on Auto Tone is also randomly unsuccessful. What's more, all of my custom presets just emptied themselves yesterday and had to be rebuilt.
Has Adobe any answers?