How often do you need to do something complicated in PowerApps and you use Flow to do this for you? When this something takes longer than a minute you might run into issues. These Long running flows called from PowerApps will time out after one minute. The Power Platform can handle long running flows, however when you call them from PowerApps you might have to do some additional work.
During one of my projects I recently ran into the issue where the flows would sometimes take longer than 1 minute. Then as I tested the solution I also found that you get the same error when you close the app before the flow has finished.
As a test I created a flow that simply waits for 2 minutes and then I called it from a Button or a Timer in PowerApps and in both cases I received the following failure
The execution of template action ‘Respond_to_a_PowerApp_or_flow’ is failed: the client application timed out waiting for a response from service. This means that workflow took longer to respond than the alloted timeout value. The connection maintained between the client application and service will be closed and client application will get an HTTP status code 504 Gateway Timeout.
In my case I was able to optimise the flow a bit and the problem went away. Of course it doesn’t stop the user from closing the PowerApp. So you might need to add some error handling on the Respond to a PowerApp or flow action.