Does undergrad score matter very much when applying for a second Masters? When applying for a second Masters, does one's undergrad score hold a lot of importance or does it get discounted in favor of better score in Master's?

Adding more information:

I have a BS in Mathematics from one of the good Indian university colleges. I spent a lot of time in my BS studying only my favorite subjects at the expense of others. I have a 66.67% in BS. Contrast this with the university topper who will be somewhere close to 90%.

I also have an MS in Economics from one of the good (in India) Economics grad schools. My MS score is decent (3.14 / 4.00). Though my batch topper scored 3.44, the typical top score from the school is close to 3.75.

I am considering applying for MS in Data Science (or CS with concentration in DS). I want to understand how much my bad score in BS will bring down my chances of getting a good school.

PS: I currently work as a Data Scientist for one of the leading analytics companies in India (will soon finish a year).
Your question is difficult to answer confidently because you don't provide information about the program you're interested in or your prior studies. What did you study in the past? What do you want to study?

Did you do well in your undergraduate classes relating to your prospective masters area? Is your most recent masters in an area closely related to that of your second masters? Did you perform well in your first masters program?

To make things easier, you should perhaps call the admissions office of the program/department you're interested in joining. Be straightforward about your situation and they'll likely be helpful in guiding you.