This happens when I am working with at least two sets of grouped objects (shapes) in a Draw document. If I edit an object in one group, the other grouped objects become inactive, cannot be clicked on or edited. They appear faded or greyed out although the dimmed colors are still there. So far the only way to work around this state is to ctrl-z back to the point when they were not faded.
It's by design, but with Ctrl+Z you undo what you have just done. Right click > Leave group
The greying out is by design, and very useful to understand which objects are part of the group currently edited, and which ones are not. You can double-click out of the group to exit the group. Unfortunately, the functionality was lost in version in a regression, see bug 122735.