I experimented a bit more and found the following workaround for using mobile internet with SIM slot 2:
By switching the network mode to “2G only”, the connection is re-established and “Connected” is now displayed under “Mobile network”.
If you then switch back to the “4G preferred” network mode, the mobile data connection remains “Connected” and the mobile Internet connection works correctly with 4G.
I tried this, and after switching to “2G only” it does say [enabled] (tho no mobile data of course), but when i switch it to “4G Preferred” the phones switches back to [limited connectivity].
Also find that when i restart the phone with the sim card inside it updates the Mobile Network > MMS Access Point Settings from what is shown in the screenshot to:
Connection Name = talkmobile.co.uk (minus the “payg.” prefix)
Authentication = “None” (rather than “PAP or CHAP” + “wap/wap”
Proxy address = “212.183.137.012” (they added a zero in the fourth character group)
Settings which still don’t work.