Family sharing / content restrictions resetting independently.

We use family sharing for our two children and have never had a problem until this week.

We set our children's "content and privacy restrictions" to "only approved websites".

Over the last 48 hours one of their devices keeps resetting to "limit adult websites".

Not only is this annoying, but our list of "approved websites" is lost every time and needs to be re-added.

I am confident the child has not hacked the iPad code because it resets even when sat unused in an empty room!

From looking on this forum, this has been a known issue for some years. I have tried all the resets suggested including updating everybody's iOS, and turning screen time off and on again. The option to make account changes is turned off.

Any advice much appreciated - this is meant to be one of Apple's selling points!