Vivaldi 6.8.3381.53 stops to run under linux Gentoo

[cnervi]

Hello,
I've been using Vivaldi in linux Gentoo regularly.
After the last Gentoo update (If I understood correctly dev-qt/qtbase-6.7.2-r3) Vivaldi stops to works.
It runs the initial screenshot (with the profile), but then disappears.
vivaldi-bin continues to run, but no display is shown.

I'm using the last updated Gentoo and nvidia-drivers.
Any help would be greatly appreciated.
Thanks!
Carlo

UPDATE: it seems a problem limited to the initial selection of a particular profile. Selecting another profile works again...

UPDATE 2: after accessing with another profile and playing with profile management, all the profiles are now working correctly. Don't know what's happened...