Apologies for the late reply. It is indeed due to iOS 13’s auto capitalization.
When auto-capitalization is enabled and about to capitalize your next character, pressing “Enter” will cause iOS to send a “Shift+Enter” combination instead of just “Enter”.
Unfortunately there is no reliable way for us to detect whether the “Shift” key is held down by the auto-capitalization or your external keyboard. We had to resort to ignoring that key to ensure the app continues to work on iOS 13.
If you know of a good way to handle this issue, please let us know. It’s been frustrating for us as well!