BT Broadband changed from VC-based to LLC-based

Yesterday my BT Broadband was working fine, this morning no connection !

Having tried rebooting the router a few times, I reran the DSL setup wizard.

The connection type changed to LLC-based PPPoE
rather than the previous VC-based PPPoA

Now back online.

I thought BT always used PPPoA?
What changed and why?