A plot problem, or plot stall, or writing yourself into a corner, is when you're going along pretty good, writing your story, and you suddenly get stuck. You don't know what's going to happen next. Or the thing you wanted to have happen next doesn't seem to make sense anymore. The story was going along smoothly, now it's all awkward and bumpy and wrong. You will find yourself having to explain why characters are doing things they are doing, coming up with elaborate justifications for actions that you know in your gut are out of character. Hand waving things that really don't work. And then you may just hit a point where you can't go on.
It's not that you're lazy and you don't want to write, you're not blocked, it's that you know something is wrong and the plot path you are on doesn't work anymore. It doesn't feel right. It doesn't match the image of the story that is stored in the back of your brain somewhere. Whatever it's supposed to do, it's not doing it.
The reason a lot of writers and artists watch Project Runway is to listen to Tim Gunn's tutorials. He's been a teacher and a mentor to creative people for a long time, and a lot of what he says can apply to any artistic project. One of the things he will tell people is, to paraphrase, "you need to free yourself from this" where this is the thing you've worked yourself into a corner over. That means you need to step back from the flawed thing you have been trying to fix and mentally start over. Your basic idea is probably still good. But somewhere along the way you went off the track from it.
The longer the work, the more likely the plot problem doesn't originate at the point where the story-car slid off the road and your writing came to a halt. The plot may dead-end in chapter six when you realize this is just not working, but the groundwork for chapter six was actually set up in chapter two. Chapter Two is where your problem starts, not chapter six. You need to stop hammering at chapter six, trying to make it work, and think about how you got there.
Take a fresh file or sheet of paper and start outlining the plot so far, in simple declarative statements. "Janine wakes up, discovers someone has broken into the cargo hold of her airship." "Janine calls Esther for help, and they find footsteps and follow them out of the compound." etc.
Just outlining it like that may help jog something. Are Janine and the other characters taking the next most logical step to figure out their problem? Did they/you make an assumption somewhere that doesn't make sense? Is the solution too easy? Is the solution too complicated, because it's trying to fill in plot holes that shouldn't be there in the first place? Are you making the characters do what you would do rather than what they would do?
Maybe Janine should call the airship police, maybe that's really her next most logical step, maybe it's the natural thing for her character to do. If there isn't a reason she shouldn't do it, maybe she should. Maybe it will add a layer of complexity to the plot that will lead you to the next step, and open up more interesting possibilities.
(There's a bit in Dorothy Sayers' Gaudy Night where Harriet is working on her book, dictating it to her secretary, and she is trying to write a scene where a guy, Wilfred, finds the murdered man's handkerchief in his girlfriend's room, and assumes she has it because she's the murderer. The scene just won't work, and finally the secretary says, "If that happened to me, I'd assume the laundry just made a mistake." Yeah, pretty much. Wilfred isn't going from A to B, he's going from A to M, and most of the readers are going to need a willful effort to follow him on that journey. It just doesn't make sense. Harriet solves this by going back to the beginning of the book and making Wilfred the kind of person who would naturally make the assumption, on very poor evidence, that his girlfriend is a murderer.)
If that doesn't help jog something, look at the individual plot elements. Are there any that make you, in your heart of hearts, go "blegh." Are you actually stalled because you're really thinking "I don't want to write this part because it's boring"? This isn't a report for work, it's fiction. If it bores you, it's going to bore your readers. Get rid of it and think up something better. Maybe you picked the easiest thing, the first thing you thought of, when you should have pushed yourself and picked something different, trickier, edgier. Maybe it shouldn't be Janine's airship, maybe it should be her sentient flying whale.
If that still doesn't work, try explaining your plot to someone in person or email. When you're thinking about a plot, telling it to yourself, you can unintentionally gloss over the tricky bits that don't work and they slip past. When you're trying to make another person understand what you're talking about, those tricky bits stand out like they're lit up with neon.
But basically the key is, for me anyway, to step back. If you're trying to get through a maze and you come to a dead end, you go back and look for the first wrong turn you took, you don't stand there pressing your body into a hedge trying to will the pathway to appear.