Altium 17 Backdrilling not working on some vias

[dmg]

Hi,
I'm working on a design that requires backdrilled vias on altium 2017.I was trying to use the new feature to ease the backdrilling definition and report I've defined the rule to target them and the corresponding backdrilling pair according to altium's documentation and it does automatically recognize most of the targeted backdrilled vias, but not all of them. Some of the vias don't get recognized as requiring backdrill and I don't know why, as they have the exact same geometry, net class and starting-ending layer as the other vias that do get backdrilled. I've even substituted some of these vias for copypasta'd vias from others that get recognized as backdrilled, but to no avail.

Even on vias on the very same net that are very close to each other, one gets recognized and the other doesn't. Exact same geometry and layer stack on both.

Anyone got any idea on what might be the issue?