It says "serialization has resumed" on the first page, so I assume that it was probably canceled/on hiatus for a while, and then was given the opportunity to finish cleanly in 3 chapters. Which would explain the timeskip and the dramatically improved art -- the last few chapters before this one were very heavily chibified, suggesting a first time serialized author who couldn't keep up with the scheduling rigors.
To be honest, while I love this mangaka's oneshots (they're on Dynasty Scans if anyone's looking), I wanted to like this one much more than I actually like it. It has its charms: the Rocker Girl is the Rockiest of all Rocker Girls ever seen in manga, with style and attitude to match, but wow is she -- and everyone else except the poor, tortured, traumatized MC -- a pushy bitch.
In any case, thank you to the scanlator for taking the initiative to finally finish this work. Heroics.