Cannot unlock Local Items keychain
I know my keychain password. Using it I can unlock the Login keychain and the system keychain, and I can change the keychain password. At the moment it is identical to my Login password.
But when I boot I get several popups asking me to unlock Local Items by entering my Keychain password. My valid password is not accepted. And in Keychain Access my Keychain password is NOT accepted for unlocking Local Items. An example:
In the old days I would have run Keychain First Aid, but that is no longer available.
Running Sierra, latest version including recent security update. This problem is new, since a recent update. I am not afraid to use Terminal if necessary to try to solve what appears to be a limited corruption issue. I would strongly prefer not to throw away the current keychain.
MacBook Pro, macOS Sierra (10.12.6), 15 inch, 2.6 GHz, 16GB RAM