Likely my fault, as I had been monkeying around with Screen Schemes prior to all of my issues disappearing from the Kanban board, but the issues look fine when I view them directly, and there's no obvious sign of error.
My Kanban board (and backlog) now tell me no issues exist.
However, if I go to "Board settings" I see all my issues in their correct columns with accurate issue counts. There are no statuses in Unmapped.
Similarly, the filter view shows all issues as expected.
I've tried creating a new board for my project, and that is similarly empty.
I've tried editing and resaving the board filter, no improvement.
Some online discussion that seems somewhat relatable suggests reindexing may be the solution, but this is no longer available with Jira Software Cloud. Hopefully it's something else -> https://community.atlassian.com/t5/Jira-questions/Kanban-Board-Empty/qaq-p/619373
Any help appreciated, thanks!