Taken from the Zoom Press release:
“We have recently detected an issue with the Handy Recorder app and iOS 11. The Handy Recorder app does not startup properly on iOS 11 which is slated to be released on September 19, 2017.
If you are currently using the Handy Recorder app, we recommend that you do not update to iOS 11 for the time being.
Please check back for updates on this issue. We apologize for any inconvenience.”