It has happened to me on two previous iPads And this one. My recollection is each occurrance was while trying to use a cellular connection. The Genius bar, unable to figure it out, just handed me a new Pad (sometimes paying the additional warranty fee pays off). But I digress.
When it happened on this one I recall utilizing the “Personal Hotspot”. Additionally, I may have had to invoke another choice. All of this took place a few years ago, thus my uncertainty. Anyway, after that, I had no problem accessing the web via cellular.
Here’s another idea: Have you selected “Allow Safari“ and other apps to run via cellular connection? It may be worth checking. BTW, after getting the cellular connection to work, the “Personal Hotspot” was deactivated without issue.