Bug report: iOS help chat window closes keyboard entry

iPhone X, iOS 11.1.2, Monzo 1.9.19

Writing a support request in the help chat. After about 8 lines the keyboard closes and tapping in the text area shows and then immediately hides it. Entered text persists between visits so only way to clear text was to submit it - managed to add a few random characters as the keyboard showed and then hid but not to delete enough to solve the problem.