Only blank page for Main-UI on older iPad 4

Hi there, I had an openhab 2 installation before, not that big one. Only some rollershuters and sensors. That worked fine for me and I had an older iPad as a dashboard on the wall with HABpanel.

Now, I would like to try out openhab 3 and installed this completely new from scratch via openhabian image and new SD card to my raspberry pi 3 model B+ acc. to documentation. Everything works fine and I can access the new main UI via my Windows PC, newer iPhone etc… Only the access via my older iPad (that I would like to put on a wall again) only shows a complete blank page. It is a iPad 4 with iOS 10.3.3 (no further update possible) and I have tried different browsers (Safari, Firefox, Kiosk Pro Plus…). Other simpler UI’s (basic UI, HABpanel) are accessible. Are there some special requirements for the main UI to access? What can I do to get my old iPad compatible? It would be fine, if someone has an idea.

Thanks in advance and regards, Peter