I’ve had a similar experience, recently. After a hiatus of several yrs I've returned to my Atlantean-Lemurian series. Was a little slow getting started, but once I re-immersed myself in the antediluvian environment of the previous stories, the new novella began to pick up speed.

I do enjoy finishing incomplete stories, or working on variants of existing stories, but only if the styles are compatible (and I have permission). For me, this works best if there is somewhat less detail in the original story than I would put it, leaving room for my own spin on it.
Sometimes I just write Marknew versions that are inspired by the original by are wholly mine.
I love writing Marknew variants with Steve the Z's stories, and Helplesscase has inspired two entire stories for me.