Hi Ryan,
Looks like you have run into a bug. Though I am unable to reproduce the issue you describe with my own data/map/layout, I can think of no reason for this behavior outside of a bug. If you can, please take this issue to technical support.
In the meantime, you can select the element you want to work directly from the Contents pane (the TOC). If you want to select elements interactively you can use the lock functionality to keep from selecting elements you do not want to select.
Here is a paragraph describing lock from the help topic Layouts in ArcGIS Pro—Layouts | ArcGIS Desktop
Once added to a layout, elements can be selected, moved, and resized on the layout to achieve the desired look and feel. This behavior can be turned off by locking an element, preventing selection, moving, or resizing interactively on the layout. Switch between locked and unlocked views by clicking the Lock button next to the element in the Contents pane.
Hope this helps.
Tom