I am using the pattern tool, and I am sure it works well for filled objects with no stroke, but when I try to tile a pattern which uses stroke, it treats as a visual bounding box, not a geometric one (even though I have setting Preferences > Tools > Geometric bounding box enabled).
What this means is instead of the pattern tiling correctly, there are gaps at the joins, as shown by the red circle below:

Notice how instead of the centre of the strokes touching, the outside or the strokes touch, hence the lines do not line up perfectly.
A workaround would be to convert the stroke to paths, and clip the edges, that makes the image larger, and is move of a hack than a fix. I have also tried changing the stroke caps, which did not help.