Recently when I was asked to log back in to askubuntu, I got taken to a different launchpad page that asked me what kind of access I wanted to give to askubuntu, including access to modify private bug reports. I don't want to give askubuntu any access on launchpad, only use the OpenID to authenticate me. I opened this question and was told that askubuntu removed support for OpenID and is now using OAuth instead. Why was this done? It seems like the wrong thing to do.
Of important relevance is that OpenID support is in the process of being fully disabled across all of StackExchange, with a final kill date for OpenID support of July 25, 2018.
The Launchpad OpenID support changes were rolled out more quickly here for Ask Ubuntu because myself and some other individuals are part of the Teams system being rolled out on StackOverflow, and OAuth support is needed for that to work (the OpenID logins were 'disallowed' if you were part of Teams). You probably got caught inside this rollout.
Also of note: Launchpad login is only officially supported on the Ask Ubuntu site specifically. It is not a network-wide option for logging in. As such, the Launchpad integration has already been moved to OAuth based login credentials, and this was done back in late May, and is a StackExchange driven change, not an Ask Ubuntu specific change.
Technically OpenID support for LP logins by providing the OpenID 'works' until the complete phaseout happens, but the LP login endpoint with the "Login with Launchpad" button now points to OAuth and not OPenID. So you will need OAuth to use the "Login with Launchapd" button now.
You will need to disassociate the OpenID login, and associate the LP login again with OAuth to restore LP login functionality. (Details of the phase-out network-wide are at the link above). And when you link it again, you can use the 'Read non-private data' option, so that SE can't write your data or anything, and can't see your private data either.
According to Nick Craver of the StackExchange staff, they are in the process of sending out email messages to users who only have OpenID login credential methods to add alternative methods of logging in with credentials to their account.
They have also altered the OpenID Support Final Death Date to be July 25, 2017, exactly one month from today. Which means you must now alter your login credentials so that you are not relying solely on OpenID to login to your account.