Hi. As stated changes were made to NTP ads delivery. See related post below. I think the changes were first implemented in the 1.41.x version…
Also, can you post your current version? The current version of Brave for Android is 1.43.89. I think there were changes to how brave fetches the ads catalog in 1.43.x. If you are not receiving any NTP ads at all, and you are not on version 1.43.x, check that all the components listed at brave://components are up to date. However, if you are on an older version, I would highly recommend that you update to version 1.43.x as ads are phased out for delivery to older versions of Brave.