The bunched ones will be freshly launched batches of satellites that have not reached their target altitude, they will spread out in the process.
The latitudes that they overfly are currently limited to up to 53°. The explanation might not be the easiest but here it is: satellites go around in a circle or ellipse that lies on an imagined plane, the so-called orbital plane [0]. This plane can be at an angle with the equatorial plane which is called the "inclination" (this value also gives the maximum latitude that they reach). Starlink uses a lot of these planes, each rotated a bit further around the globe [1]. This is so that all areas on the ground will be in sight of one of the satellites eventually. Starlink should also be able to function a bit further to the north than 53° latitude right now but for any latitude much higher than this, users will need to wait until SpaceX has a working network in polar orbits (i.e. not flying on these tilted plains but more or less directly over the poles instead). They are required to eventually serve Alaska, for example.
[0] https://en.wikipedia.org/wiki/Orbital_plane_(astronomy)
[1] https://en.wikipedia.org/wiki/Longitude_of_the_ascending_nod...