SNAP bursts boundaries coordinates NaN values

Dear All,

I am performing a classical S1 SLC processing on SNAP. I am applying subswath splitting,precise orbits, radiometric calibration, de-bursting, multilook, terrain correction and radiometric normalization. I am interested for each of the processed subswath to retrieve the bursts boundaries coordinates from the metadata. In some cases it is successful…in other cases I get NaN values. In all the cases I have seen so far (around 10 processed images) that happen only on the last burst.
What could be the reason for that?

Here I attach an example of when it is working and when not.