[VB-34835] Authorization on main page

[kurai]

I visit my blog via the link from the speeddial ( https://kurai.vivaldi.net ). Often, the main page requires authorization. I press the login button and after authorization is loaded not the main page of the blog, but the page of the last entry (on this moment this page is https://kurai.vivaldi.net/?p=540)

[kurai]

What it means?

[LonM]

I have experienced this error when I try to log in the see the blog pages. If I just re-open the main blog page it goes away. I'm not sure what the problem is, exactly.

[LonM]

This is still happening, so here's a more detailed report:

Actions Taken
I have this in a web panel:
https://lonm.vivaldi.net/wp-admin/index.php?page=msreader.php
(accounting for whatever your username is)

Every now and then (about once a week) I get logged out

Loading the web panel takes me to this log in screen
https://login.vivaldi.net/authenticationendpoint/login.do
This has the following parameters (I have redacted some of them):
client_id=4c3PVUVREDACTEDSc9f7_u_Hr_cka
&commonAuthCallerPath=%2Foauth2%2Fauthorize
&forceAuth=false
&passiveAuth=false
&redirect_uri=https%3A%2F%2Fvivaldi.net%2Fwp-admin%2Fadmin-ajax.php%3Faction%3Dopenid-connect-authorize
&response_type=code
&scope=openid
&state=87833d62REDACTEDc837d6cd0d
&tenantDomain=carbon.super
&sessionDataKey=e0831644-REDACTED-01a43f7f8a22
&relyingParty=4c3PVUVREDACTED_u_Hr_cka
&type=oidc
&sp=Vivaldi.net
&isSaaSApp=false
&authenticators=BasicAuthenticator:LOCAL

Enter authentication details
Click login button
Login button changes colour

Then, I get directed to the error page shown above:
https://vivaldi.net/wp-login.php?login-error=missing-state&message=Missing+state
This doesn't make sense, as if you look at the original oauth URL above, you can clearly see that a state is set.

At that page, click "back to vivaldi community"
You are not logged in

Click home button in the web panel controls
You are logged in

And to top it all off, if I go to vivaldi.net in a tab, I am logged in, despite being just told in the panel that I was not.

Additional Details:
Vivaldi 1.16.1177.5 / Chrome 65.0.3325.183
Not blocking third party cookies
Accepting all cookies from vivaldi.net