I just did watch the episodes on TV when I had the time, so I'm not really deep into it. From looking it up the ending I mean is called "Sleeping in light" so Season 5 i guess?. I think I need to do a rewatch and watch it properly this time.
Then unexpectedly got a season 5, but weren't sure if there would be a season 6, so ended up hedging their bets with an odd season (compared to the others).
And then the post-show movies provided a few more opportunities, but never evolved into follow-on series.
Sleeping In Light was always intended to be the finale; once season 5 got secured they shot another episode (which was also great) to act as season 4 finale.
The uncertainty with season 5 did play havoc with the pacing of the arcs. Season 4 did have to cover a lot of ground to get the most important arcs to close, so parts of it feel rushed, and vice versa the beginning of season 5 takes a while to get back to speed. Sigh.