@peak4 This has happened to me twice since the update. On my desktop it did it quite soon after the update - I hadn't stored my tabs as speed dials - but the first thing I did when I booted my laptop up was save all my workspaces as speed dials. I still don't have all my workspaces back to how I had them. Gutted.
It then happened on my laptop a few days later. I recovered all my workspaces by opening the speed dials. After I recovered them all, I closed Opera and re-opened and it had lost them again(!)
This isn't good at all and I hope that there's a fix soon.