From reports gathered, it appears to focus on HOME accounts that has been accessed by various different users.
Doesn't look like bans were issued outside of that period.
Besides colloquial evidence, and knowing it's high traffic accounts, there are a few conclusions we can draw.
Maybe it's HOME accounts that were accessed with a lot of different Switch console IDs.
Maybe it's HOME accounts that has high volume of network traffic.
We can't confirm if it was exactly IP, since we don't work for them. All we could do is spread the word on the preliminary finding, so that users can avoid falling into such situations.
It shall also be known that I know a lot of people with illegal mons in their HOME account, that didn't get banned, possibly because of them not account sharing.