I figured it out.
I've been puzzling over the missing piece in my current novel in progress, making very little progress actually.
It wasn't exactly a sagging middle.
And it wasn't only the lack of kick ass action from my main cop character.
Until, in a quiet moment when I was thinking about something else totally unrelated, maybe what to fix for supper that day....
...boom, the door opened! There it was! The missing piece.
A scene that could have been interesting and tense had been watered down....because it happened in the wrong setting and was narrated by the wrong character.
It has taken a few weeks to sort it out, and I've already done most of the writing in my head. Now I'm getting it on paper and revising all the stuff around it so it fits.
Many times I've said I don't get writer's block. That's sort of true, because I always have new ideas for the next project. What I do get, I guess, is plot block on the current manuscript. I can see something is wrong (sometimes with the gentle help of my critique group), but it takes time to discover the fix.
And then it happens.
And then I fix it.
And then I'm done....until the next time.