Moldova
In 2006, Zdob și Zdub finished 6th with the catchy song Bunica Bate Toba. That was the country's debut at the Eurovision Song Contest, and in the years that followed, they would show several times that they managed te catchy songs very well. In 2008, Moldova failed to reach the final, but they got quickly back on track, and it wasn't until Cristina Scarlat's participation in 2014, they again missed the final.
2014, however changed things. They country had lost their ability to send catchy songs. Their entries sounded too much like what we heard from other countries, and for three years in a row, Moldova didn't manage make it to the final.
SunStroke Project returned to the contest in 2017, after they finished 22nd in 2010. Hey Mamma was yet again a very catchy song, and Europe fell in love. They came in third, and secured the country their best ever result.