Secure Score: I just don't get it

I think you are following the right steps, so it's just a case of persisting I think and seeing if Secure Score starts registering the points.  Each report does have to be initiated regularly from Secure Score for them to be seen and counted, within the timeframe mentioned. 

For 'Review mailbox forwarding rules weekly' it considers running the PowerShell script to be required at least once a week, for good measure, run/schedule it every six days perhaps and see if that follows through with adjusting the score.  I think it could be clearer with what exactly triggers the points with this measure, as the Audit Log Search can also be used as well to find this information.

Browsers should not make any difference.  If the scores still persistently don't match with the actions you are carrying out, it might be worth opening a service request, if nothing else is forthcoming!

Big fan of Secure Score here as well but it does occasionally show irregular results, at least I have noticed that recently on a dev tenant, that corrected itself afterwards around a week later.