I’m not sure why Microsoft choose configure the firewalls they way they do but there is certainly options disable/enable based on private/public networks. The issue in this case, not for the first time, is that their update has overwritten customer settings causing problems (at a particularly inconvenient time for me).
Yes, it is just a matter of reconfiguring the existing firewall but, if it was already disabled you might not check it. The point of my post was to raise awareness as many people disable WIN10 firewall and use alternatives which are generally far better performing.
I shall now permanently block automatic OS updates.