okay I could solve it. No idea how that happened, as said I could launch the SZ from the gadget button but no browser launching and the browser shortcut there lost its icon + no SZ tab in Avast UI.
So I checked the change menu from the uninstall entry and SafeZone appeared there as not installed
I checked the SZ entry, rebooted and now it works again as expected.
edit: the browser starts now automatically when launching the SZ, but minimized, no big deal.