dps66678 Thank you for explaining in detail! And I'm sorry, but when I wrote my first reply, I thought the dopesheet filter was turned on, but it seems that the Sync button is actually turned on, and I can see that this is the result of the Sync button.
When the Sync button is enabled, the dopesheet shows the rows for the curves that are visible in the graph. In the graph view, the slot attachment timeline is not displayed by default (because the slot attachment key does not have a curve). Therefore, when you select the root bone, the slot attachment time line is hidden in the graphics view, and even if you select a bone after that, the slot attachment time line remains hidden in the graphics view, because the display in the graphics view is managed by the display in the dopesheet. If you do not want this behavior, disable the Sync button.
