Migration to 6.x fails without error

I recently upgraded to 6.1.4 (on WP 6.1), clicked the Migrate Formats button in the settings which then shows the “You nave successfully migrated to the default v6 formatting options, enjoy! We have an undo option, just in case…” message – but that box asking me to migrate never goes away.

There’s no error in the JS console when clicking the migrate button or anything else which would look suspicious.