The Ohio Board of Professional Conduct has issued an advisory opinion which reiterates three basic and uncontroversial principles on conflicts of interest. The opinion is Advisory Opinion 2019-01 and you can read it in full here.
The opinion makes three points:
First, the opinion states that, absent informed consent, a lawyer may not undertake representation of an adverse party in an unrelated matter when the lawyer represents current clients with claims pending against the adverse party. This conclusion should not be surprising. It is just the basic principle against concurrent conflicts of interest expressed in Model Rule 1.7.
Second, the opinion states that a lawyer may not withdraw from the representation of a current client in order to undertake representation of an adverse party, even if the matters are unrelated. This is another way of saying that the Board would apply the so-called "hot potato doctrine" which prevents a lawyer from trying to dump a client in order to "convert" the client from a current client into a former client before taking on a new client in a matter adverse to the interests of the converted former client. I can't say how many jurisdictions have formally adopted the doctrine, but it is pretty well known so I am not surprised by the opinion's position on this.
Third, the opinion states that absent informed consent, a lawyer may not represent a former adverse party in a new matter against a former client if the new matter is the same or a substantially related matter in which that person’s interests are materially adverse to the interests of the former client. Again, this is not news since it is simply stating the basic principle regarding successive conflicts of interests expressed in Model Rule 1.9.