I have a skill that starts off with a progressive response (retrieving your details please wait).
I then kick off the transaction which takes a couple of seconds before returning the results.
On an Echo device, this is handled correctly - I get the progressive response spoken, followed by a short delay, and then the final response.
On non-Echo devices (Sonos One, updated iOS Alexa App, Simulator), I request the skill, get a delay whilst the results are being retrieved, then the progressive response followed immediately by the final response.
Is this a known issue - I know its documented as happening on the simulator but haven't seen any it for other devices?