If it's any help, here's some more details about the fault.
Phones are both Galaxy Note 3 and Galaxy s6 edge (same problem on both). Both running Android Lollipop.
I have around total 25 speed dials organised in 6 folders.
To reproduce it's just to log in to Opera sync and then normal use of Opera. Starting, browsing and then closing on both phones. With normal use, within a day or two, suddenly the speed dial folders are all messed up like I described earlier. It's pretty consistent. It's just a matter of time when it happens.
Hope it helps