Thanks @Steve@devon
It's definitely the iOS app causing the issue. Another iPad I have still has version V4.5.0.645512 on it and works flawlessly.
The iPad Mini has been upgraded to V4.7.1.811812 and suffers the issue with the timeout. From the App Store, it looks like 4.7.x is about 3 weeks...
I'm getting the same issue, but had not upgraded the firmware; it just suddenly started happening a week or so ago. I don't think it corresponded to an iOS update as its running on an old iPad Mini that doesn't get regular updates any longer. There may have been a Hik-Connect update as I have...