Unexpected data transfer from APS3 to USE1

In my Jan 2024 bill, I see an unexpected charge for data transfer (8 GB+) between two regions - from APS3 to USE1, which is Asia Pacific (Mumbai) to US East (Northern Virginia). I actually don't run anything in USE1, my public website is setup in APS3. So the only expected data transfer is between APS3 and the Internet using HTTPS. My web pages don't transfer any huge data – max is a few MB.

1. I asked Customer Support to check what account, the destination IP address in USE1 belongs to. If it is not my account, I feel that someone may be trying to exploit my setup (or am I wrong here??), and they should act on that account user. They say that they cannot provide the info.

2. I see similar transfers happening this month (Feb) too – not always, but randomly. I saw something called Flow logs in AWS for this purpose. This repost also talks about the same. I run Ubuntu 20.04 LTS – is there anyway to log network requests in Ubuntu for this purpose? In fact, it would be nice, if I can track only requests coming from USE1. What is the best way forward?