There seems to be a bug with the chat system + Siri Text to Speech while using the ROBLOX app.
While testing, the bug crashed the app 100% of the time by clicking the “Chat” button inside the app, then clicking the Text-To-Speech microphone button.
Multiple levels have been tested and the issue appears in all games. I am unsure of when the bug started happening as I rarely use the iPhone app. When I do, however, it is much easier to say what you want to say on the iPhone, than type it.
iPads were not tested and the various iPhones tested were running iOS 7.1