Datetime error: undefined is not an object (evaluation 'this._appRoot._getPortal'

Hello all,
I’m using ionic v3.9.2. I want to implement the ion-datetime component in my Page. If I want to open the dateTime Page I get the following error:

TypeError: undefined is not an object (evaluating 'this._appRoot._getPortal')
present — app.js:241
open — datetime.js:384
_click — datetime.js:347
(anonyme Funktion)
callWithDebugContext — core.js:15098
dispatchEvent — core.js:10004
(anonyme Funktion) — platform-browser.js:2628
onInvokeTask — core.js:4751
runTask — polyfills.js:3:10845
invokeTask — polyfills.js:3:16802
p — polyfills.js:2:27655
v — polyfills.js:2:27895

Can anybody explain why I get this error?