I noticed the x-sheet layer button icon displays 2 rows below the very last drawing you have in the layer, making them invisible in the layer with most drawings of the scene or when creating a new scene.
1. Activate Show Buttons in X-Sheet > Active Layer > What To Display Beyond Last Drawing > Show Buttons
2. You can create a new scene or check in the one you are working, the button icon is hidden for the layer with more drawings.
Actually this is correct behaviour! It is on purpose that the longest layer does not have the button, because basically it does not technically make sense to be able to change what is beyond the last frame. Since the scene ends at that point anyway.
However! I must admit reading your post, that this might be confusing. Maybe it is better to have the button to avoid this seemingly weird behaviour. Also when the layer is not the longest anymore, you could have set the button beforehand if it existed.
On the todolist for careful consideration! Thank you!