“It goes like this: describe – in detail, with precision – some architecture, someone’s clothing, something in your POV character’s visual field.”
The fun scenes are done and you’re stuck with filling in all the gaps. You have three choices: slog, panic, or start something new. Unless there’s a way to rekindle the fun..
I think the problem of plot snarls is a lot like knitting: you’re continuing merrily along, sometimes with a pattern, sometimes just making a big ol’ scarf, and you get to the end of a line and realize you’re missing a stitch.