Do a test. Download the Opera installer, launch it, click "options", set "install path" to a folder named "Opera Test" on your desktop, set "install for" to "standalone installation", uncheck "import data from default browser", and install. Test in that Opera, but do not install any extensions, do not enable Opera Sync, do not import anything and do not enable Opera's adblocker and tracking protection.

Does it work fine in that Opera? If so, goto the URL opera://bookmarks in your regular Opera and export your bookmarks to an HTML file. Then, goto the URL in the test Opera and import the HTML file.

Does it start happening then? If not, goto the URL opera://about in each Opera and take note of the profile path so you know where the profile folders are at. Then, close down both Opera's and replace the "Bookmarks" and "Bookmarks Extra" files in the test Opera's profile folder with copies of the ones in your regular Opera's profile folder. Then, try the test Opera.

Does the problem happen then?

Are you using Opera Sync to sync your bookmarks?