iPad "Mobile Data Number" shows as "Unknown": Why?

As per the title, I have three new-ish iPads (two M4 Pro's, one Mini 7), and they all have pre-paid eSIMS in them from UK network Three – the "24 Gigs for 24-months" physical pSIMS you can buy online, that I had to call customer services, who then converted them all to eSIMS a couple of months ago (as the iPads only have eSIMS now).

I noticed that whilst data works fine on each iPad, annoyingly I cannot see the data eSIM's actual number in the settings where it used to show with previous identical pSIMS — under: General > About > Mobile Data Number it simply says "Unknown".

While I know this is nothing to do with messages and related features which are pushed from my iPhone, it's still really annoying when I do something like phone Three's customer services or similar reasons like wanting to check my data allowance left, and cannot simply check the data phone number in this section anymore, because it's simply not there.

I first phoned Three a couple of times (who were clueless!) and they didn't have any ideas on why it was showing "Unknown" (my Network Provider above this section shows "Three 63.0" if that's pertinent here?).

Is there any way to get the number to show anymore? If not is there some reason for it to not show?