When using the least-dense brush fill and zooming out one level on the map, you can create a confusing visual situation where a tile that is "full" with dots will be sub-sampled to a completely empty tile on some zoom levels, and a completely FULL tile on other zoom levels. Examples below.

Zoomed out one level.

"Base" zoom level.

Zoomed out two levels.

Not totally sure the answer here, but perhaps there's a way to shift the sampling patterns so they're slightly misaligned with the brush patterns.

Not a huge deal! Just a strange pseudo-bug where I'm painting with a tile and it seems like it's not appearing at all.