The z–index property in the walk-through builder controls the vertical stacking order of elements that overlap.
The higher the z–index the closer to the front it will appear. If your walkthrough bubble appears below an element in SharePoint, put a large number, such as 1000000, in the Z-index field under Advanced Properties in the Walk-through editor.
This will stack the walk-through bubble above the SharePoint element. You are more likely to come across this need with SharePoint elements that appear in modal format (a dialog box/popup window that is displayed on top of the current page).
If you find that your walk-through is skipping steps, and you are selecting elements that are in a pop-up window, try adding a delay to the step that is being skipped. If the target element a step is associated with hasn’t had time to load, the walk-through will skip that step. Setting a delay will solve that problem.