The word is ketchupeffekt.
That's ketchup, as in the red condiment you might eat with chips (or, if you're Swedish, drizzle over spaghetti in lieu of sauce), and effekt, meaning 'result' or 'consequence'.
It's used to describe a situation or event where not much happens for a long time, and then a lot happens at once. The significance of ketchup will be clear to anyone who has ever tried to pour the sauce from a glass bottle — usually it takes several seconds before any comes out, and then you get a huge amount.
Ketchupeffekt is often used in a sporting context, for example to describe a game or match with no goals for the majority of the time, and then several in the last few minutes, or a team who have an unremarkable season and then multiple spectacular wins in their final games.
But you could also use it in many other contexts: for example if a lobby group has spent years campaigning on a certain issue and suddenly several changes are made as a result, or a product is under-appreciated for years before a sharp rise in sales and publicity.
Note: The Ketchup Effect is also the title in many English-speaking countries of a 2004 Swedish teen movie, but the phrase has a very different meaning in the film, in which one character likens a specific sexual act to using a ketchup bottle.
Det känns som om det blivit en ketchupeffekt
It feels as if there has been a ketchup effect
Det blev ketchupeffekt för hemmalaget
It was a ketchup effect for the home team