Issue with Pen Tool selecting border of entire project and deleting selection

When you notice the feathered line appearing around both the selection and the outside of the entire image, it usually indicates that the selection might be inverted or that an adjustment to feathering or anti-aliasing was applied differently than before. One quick thing to try is to go to Select > Inverse after making your selection to see if the correct area is being masked. Also, check the feather settings in the “Select and Mask” panel or the options bar when you’re creating the selection—sometimes feather values carry over from a previous project and cause unexpected results. Resetting the selection tools (right-click the Pen Tool icon and choose Reset Tool) can also resolve random changes like this. If nothing else works, try resetting Photoshop preferences back to default, which often fixes sudden unexpected behavior.

5 years later, ChatGPT appeared :

Fix: After making the selection, go to Select > Inverse (Shift+Ctrl+I / Shift+Cmd+I) before applying the mask, or check the "Invert" option in the "Make Selection" dialog.

You very likely want »Exclude Overlapping Shapes«. 

But why the Selection anyway? 

If you apply a global Feather a Vector Mask would work just as well. 

»It changed randomly one day«

It seems more likely that you accidentally changed the Path Operation. 

Please provide meaningful screenshots with all pertinent Panels and all the Path elements selected so we can see the Path Operation setting in the Options Bar.