401 Unauthorized when trying to log on to Openshift 4.5 with Google identity provider

I recently deployed a version 4.5 OKD cluster and everything seems fine, but I can't get the Google identity provider to work for signing in. I followed the instructions here, but with no success. When I try to log in with my company google identity I get a very generic error message:

login error

I ended up with the following OAuth config:

spec:
  identityProviders:
  - google:
      clientID: <my-ID>.apps.googleusercontent.com
      clientSecret:
        name: google-secret
      hostedDomain: <company domain>
    mappingMethod: claim
    name: googleidp
    type: Google

I set the google project up as described too. Just created Oauth2.0 credentials, call back URL (which is correct since I get back to OKD after consent screen), no extra scopes in consent; just profile, email and openid, and OKD is not requesting any other scopes. The project is set to internal so only company users can log in.

After some investigations I managed to increase verbosity on the oauth-openshift pods and here is what is seen in the logs for a failed attempt:

       1 handler.go:156] Got auth data
I0929 15:30:10.036799       1 round_trippers.go:423] curl -k -v -XPOST  -H "Content-Type: application/x-www-form-urlencoded" -H "Accept: application/json" 'https://www.googleapis.com/oauth2/v3/token'
I0929 15:30:10.071829       1 round_trippers.go:443] POST https://www.googleapis.com/oauth2/v3/token 401 Unauthorized in 35 milliseconds
I0929 15:30:10.071871       1 round_trippers.go:449] Response Headers:
I0929 15:30:10.071879       1 round_trippers.go:452]     Server: scaffolding on HTTPServer2
I0929 15:30:10.071885       1 round_trippers.go:452]     Cache-Control: private
I0929 15:30:10.071891       1 round_trippers.go:452]     X-Content-Type-Options: nosniff
I0929 15:30:10.071897       1 round_trippers.go:452]     Vary: Origin
I0929 15:30:10.071902       1 round_trippers.go:452]     Vary: X-Origin
I0929 15:30:10.071909       1 round_trippers.go:452]     Vary: Referer
I0929 15:30:10.071915       1 round_trippers.go:452]     Date: Tue, 29 Sep 2020 15:30:10 GMT
I0929 15:30:10.071920       1 round_trippers.go:452]     Alt-Svc: h3-Q050=":443"; ma=2592000,h3-29=":443"; ma=2592000,h3-27=":443"; ma=2592000,h3-T051=":443"; ma=2592000,h3-T050=":443"; ma=2592000,h3-Q046=":443"; ma=2592000,h3-Q043=":443"; ma=2592000,quic=":443"; ma=2592000; v="46,43"
I0929 15:30:10.071926       1 round_trippers.go:452]     Content-Type: application/json; charset=utf-8
I0929 15:30:10.071934       1 round_trippers.go:452]     X-Xss-Protection: 0
I0929 15:30:10.071939       1 round_trippers.go:452]     X-Frame-Options: SAMEORIGIN
I0929 15:30:10.072004       1 handler.go:176] Error getting access token: Unauthorized
E0929 15:30:10.072031       1 errorpage.go:26] AuthenticationError: Unauthorized
I0929 15:30:10.072428       1 httplog.go:90] verb="GET" URI="/oauth2callback/googleidp?state=<token>&code=<token>&scope=email%20profile%20openid%20https://www.googleapis.com/auth/userinfo.email%20https://www.googleapis.com/auth/userinfo.profile&authuser=0&hd=<companydomain>&prompt=consent" latency=35.835162ms resp=200 UserAgent="Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/85.0.4183.83 Safari/537.36" srcIP="10.129.2.28:49228": 

I can't find a reason for the Unauthorized error so any help is much appreciated.