Thanks you for all of the support that you have provided as the team worked to track down a conclusive answer to what occurred in your specific case. Your suspicion aligns with the results of the investigation, which is that your master password hash may have been corrupted during the process of server-side hashing to store your updated password.
Thanks for your patience on this one! The team did not receive any other reports on this issue but was able isolate a rare situation that may have been related, and should prevent this from happening again.