It seems like your blocks of 4x4 via stitches don’t actually connect to the copper, but the resolution is too small to see it properly.
Just recenly I saw a nice tutorial here to make via stitches by adding a component with a hole to a net.
Edit:
A search throws up many results here:
https://forum.kicad.info/search?q=via%20stitch
I think the “protip” is the one of the best.
https://forum.kicad.info/t/protip-nicer-via-stitching/1103/22