We always maintain backward compatibility with at least the previous major version (and as much as possible, with earlier versions, too).
The problem you encountered is due to that Slicer-4.10 did not take into account slice visibility attribute for markup nodes and Slicer-4.11 does (and by default slice visibility was turned off for markups).
As a workaround, you can right-click on eye icon of the markups node in Data module and check “2D visibility”, I’ve also submitted a fix that enables 2D visibility for markups by default when an old scene is loaded (it will be available in Slicer Preview Releases downloaded tomorrow or later).