Question: Why my overlay field is not working properly as the overlay file is hiding the underneath fields on template customization?
Answer: Please check if the overlay file used in the overlay field is transparent or not.
The overlay files need to be transparent in order to show the underneath fields due to the higher stacking order (101-110) set for them.
Overlay fields are rendered according to their stacking order - that is, on top of ordinal fields, just because their stacking order is greater.
Hence, to show the underneath fields properly while customizing the template the overlay files must support transparency.
Related Article: How can I create an overlay field in an eDocBuilder template?