Since 2015, Apple has one by one changed the keyboards on its Mac-products to the new Butterfly-design, a precess accompanied with much interest but also criticism. The new design helped Apple in their pursuit for thinner and thinner products, but now it seems that the new design has a reliability problem: Some users experience problems with dust and dirt getting stuck beneath keys.
https://www.notebookcheck.net/Macbook-Pro-Does-Apple-have-a-problem-with-defective-keyboards-due-to-dust-getting-stuck.258632.0.html