Struggling with pacing in the middle of my novel — everything feels flat

[fnfunkin]

Hi everyone,
I’m about halfway through my novel (a mystery with light speculative elements), and I’ve hit a wall with pacing. The beginning flows fine — the setup and inciting incident work — but once I get to the middle, the tension just drops. Scenes feel like filler, even though they’re advancing the plot logically.

I’ve tried adding more conflict and tightening dialogue, but it still reads slow. Has anyone dealt with a “sagging middle” like this? How did you keep momentum without forcing artificial action or twists?

Thanks in advance!