Finally when I reentered to my sync account on all computers (without resetting sync) - it deleted all carefully sorted bookmarks from folders. Now I see empty folders on all machines. Great!

I have three machines with latest Opera installed. On one of them I created a bunch of bookmarks for on one topic. Later, on the other machine, I moved the to newly created dedicated folder and some subfolders (subtopics).
Unfortunately it didn't sync to other machines. Even later on the machine where I originally created folders I made some more bookmarks and moved them to folders to, but on the other machines they appeared in unsorted section of bookmarks.
Can anything been done about it?

Checked. It was fixed.

https://www.opera.com/blogs/desktop/changelog-for-42/#b2393.137
Seems to be fixed yesterday. Will check later.

Same problem just upgraded from Win7 to Win10 (clean install). Installed latest opera and logged in for sync. All came up except that I can't see the Unsorted bookmarks. At work (Win7) with latest version of opera (installed two months ago) - everything is OK - I see them.
If I type in some URL from the unsorted bookmarks Opera tells me that it is bookmarked. But clicking on the Heart button opens empty popup. V7 Bookmark extension shows that all of new bookmarks I have added at work are here. Definetly something it is a bug in Opera.

Me too. Searching the web didn't help.