wifi active but Internet disconnects

I have an iPad 64gb with a cellular radio, but without a carrier selected and thus an "inactive"Apple sim. My iPad is randomly getting disconnected from the Internet every few hours - it remains connected to wifi, I can see the icon with full bars, but anything that requires internet access doesn't work. Toggling airplane mode on and off reconnects everything, and also generates a message that cellular data connection failed.

The same problem cropped up when I removed the sim altogether. Internet appears to stay connected as long as I continuously use the iPad, but if it sleeps for more than a hour or so, the Internet drops and needs an airplane mode recycle to work again. Odd thing is that the wifi remains connected, I just can't get any websites.

Has anyone else with an inactive Apple sim (I.e. One that you have not activated on any network), or with an empty sim tray seen this random Internet disconnect issue?