What is the best process for feature release and testing?

We are working on an IOT device ( HW, FW, Could and mobile app), what would the best practice for feature release process? Currently each domain ( FW, Cloud, App) develops and tests a features in an isolated manner and then we pass it to QA, so in QA when they test this feature in integrated manner end to end, we face with a lot of errors, so it seems we need to do integration development testing prior to QA. How we should do it to use everybody's time efficiently and then what process/steps you suggest for integrated development testing and passing to QA? Thanks