I had this problem also and it was driving me mad!
I finally stumbled across an old blog post with the smart group suggestion. I created that and found one file, but no matter what I did I couldn’t get it to resolve the pending status.
I deleted the file and still no luck. Eventually, I tried emptying the entire trash inside DTPO. That fixed it.
In my case, were three files that were in my NAS remote synced database but not locally. Once I deleted them from inside DTPO (yes, even from the Trash can) all started working fine.
And one of the great things of this product is it even synchronize the Trash can… that allows you to recover from a mistake. Even when you empty the program Trash, deleted items go to the macOS one…
I’m having the same error after setting up an iCould sync. I keep getting “Couldn’t upload 270 files” I’ve tried the Smart Group with “Instance is Pending” and I get 5 files in there. I’ve emptied my Trash and still no luck.
I just purchased DTG and the Premium Feature add on and set up an iCloud sync on DTPO. I have 2 databases I’m trying to sync on my iPhone and iPad. One is an import I do each week of my Apple Email called email. After setting up the iCloud sync I can see about every 6 minutes in the Activity log I see “email: Downloading Items from iCloud” and in the Log I see " Couldn’t upload 270 pending files" I’ve attached the screenshots.