I'm currently working on a telecommunication app that has 200k daily active users, 3.2k daily new users and 99.6% crash-free users for all five version build with a team of four colleagues. The most exciting part is that we have just updated the app with a full of bugs and new stuff. Struggle was the adoption of designed pages with bunch of animations spread everywhere in screen without thinking if its works on or even applicable for iOS or android mobile platforms. We've completed the project in a deadline of half of its estimated time.
On the other hand, this app has a need of a lot testing processes with eight different variants, since I worked on continuous integration in my previous job, I've created an environment for building this application's eight different variants with desired build type so that our tester can reach out and prepare the needed build.