Thanks for the thought @BLUEFROG – but no, no VPN.
I should probably clarify my issue. I had the problem when adding a PDF on an iPad into Bookends for iOS – which of course requires the use of iCloud sync. The newly added PDF then did not show up on my Macs (I think perhaps the reference did). Things seemed to work when adding a PDF on Bookends for Mac – everything showed up correctly on iPad, at least the one time I tried it.
When I hit the issue on iPad, I did do some troubleshooting (disable/re-enable the sync; rebooted things) but couldn’t get it to work. As I have never used iCloud sync for any other kinds of file sync (I don’t trust the reliability of Apple cloud anything for anything important), but have used Dropbox for years without ever having a file not sync, I decided I was going to give up on Bookends for iOS, and just use Bookends for Mac with PDFs in Dropbox and indexed in DT3, and thus also showing up in DTTG.
I can think of a few loci for the issue I encountered: (1) how Bookends works with iCloud sync (2) how Bookends for iOS works with iCloud sync (3) iCloud sync itself (4) something on my end. So I suppose the issue is not necessarily iCloud sync itself. But given that things have just worked with Dropbox for over ten years, I was not willing to spend any further time on troubleshooting.
Hope that made sense.