We've been using Jira for a long time. We had separate Jira login credentials at one time, but at some point, Jira started requiring Atlassian credentials for login. At that time, everything was fine; I created an Atlassian account and started using those credentials, and didn't have any problems accessing Jira.
In fact, I just created a new ticket in our system last Thursday, April 20. When I came back in to work on Friday, I tried to view the ticket I had created, but I was interrupted by this prompt.

I clicked "Log in using Atlassian account", and got this response:

I noticed that I had to start using Atlassian credentials (instead of BitBucket credentials) to access our BitBucket repository on Friday. I suspect the Jira problem must be related in some way.
Did my Jira account somehow become disassociated from my Atlassian account? Is this a known issue? Has anyone else run into this problem? How can this be fixed?