Sample qualifier appears to be ignored when used inside an interface block.
Similarily to the Anisotropic bug, I made simple tool to show the problem. Source: https://github.com/KrossX/misc/tree/master/gl_ssaa_block, download: https://github.com/KrossX/misc/releases/download/v0.1/gl_ssaa_block.zip. The testing program requests a 4.2 context as previously the sample and centroid qualifier were part of the in/out storage qualifier.
I have not tested linux and the sample is Windows only, and not very portable while at it. Deprecated products like the HD 5700 Series and even recent RX 5700 XT appear to be affected.
nVIDIA RTX 2080 Ti working fine as expected (no texture jaggies)
The following are samples of affected Radeon products.