Jane & Igor,
I have installed 11.0.9 & tried out some of the Transitions such as Slide, Dissolve with Blur, 3D Cube etc on a new project.
Windows 10 with the latest updates.
All seem to work OK, I have saved & reopened the Project several times.
Also moved slides around & changed Transitions back to Dissolve then back to those below the Displacement Map ones.
No problems at all.
Jane did you have your Project open when Windows updated?
Not that I can see how it would have caused this problem.
Jill