Hello SoniaBaker-445d,
Thanks for reaching out!
I did a simple test by placing a marker in my Slide Master layout but didn't encounter any behavior similar to what you described. Here's a recording of my test for your reference. The test I did is super simple and other factors might need to be present before the problem appears so I'd like to take a look at your project file to see how your markers are set up. Would you be willing to share a copy of your project file here or privately by opening a support case so for testing? We'll delete it when we're done!