The past several new releases I've tried to use the built-in updater but it always fails with the message: "Installation failed due to unspecified error. If Vivaldi is currently running, please close it and try again". This also happens when I download the full installer and try to update that way, even after rebooting and not opening the browser. To get around this I have to update in safe-mode. I'm using the x64 version on a fully updated Windows 10 Home.
Windows 10 Home
I can't really help here, I am still on win7 and really no intention to switch to win10 soon. I read many times win10 is a major PITA about installing software than MS doesn't want, and doesn't let users to set default browser to Vivaldi, Chrome, Firefox, etc. Only Edge.
Try to see if this help
Yeah. This happens to me too. At first I thought it might be my AV software, but I don't think that's what is causing it. Heres my info if it is at all helpful to you or anyone else:
Using Process Explorer I can see that something has opened a File Handle to both vivaldi.exe (and update_notifier.exe) and has locked it by the SYSTEM process. I have literally no idea what application caused this lock to occur in the first place.
The solution I've been using so far is to download the installer, unzip it using 7zip and then to manually copy the files over, as even just running the installer can cause the handle lock to occur. I also no longer install the update notifier just in case that's what the issue is. And even with all this I occasionally have to restart my computer, as the lock can randomly occur at other times.
I have the same OS as yourself.
Update worked for me on Windows 10 x64 Pro.
Perhaps the Vivaldi installer crashed/blocked because of some antivirus issue.
I can confirm this behavior. Happened to me for the first time today during update to 1.12 with the same error as specified above. Both the update notifier and standalone update methods were unsuccessful. I'm not using any AV software except for the default Windows Defender and I barely run any software in the background except for very basic stuff like media player or Steam. Windows 10 Pro x64 (1703, build 15063.608). Rebooting my computer didn't help either. I haven't tried a complete reinstall yet.