We've been working on a big application on-and-off for the last year (whenever we had time.) It was 99% working, and we left it to work on some other apps. We come back to it, only to find that some big features have magically stopped working. We dig into it and find thT some other dev team completely changed the functionality of one of the existing off-application microservices were utilizing without telling us, and then we had to spend days reverse-engineering what they did so we could retrofit our application to communicate with the microservice again.

We were able to get it fixed, but I just know that they're going to change something else in the future without telling us and it's gonna break again. A little interdepartmental communication would be greeeeaaaat!