I'm using Opera Version :65.0.3467.72 on mac 10.4.6

When trying to access to my bookmarks, when I hover over some bookmark folders, sometimes I don't get the drop-down menu allowing to access individual bookmarks. I don't understand why, because with other bookmark folders, I do get access to this menu and therefore to my individual bookmarks...

Any idea on how to solve this would be greatly appreciated.

Thanks in advance