Polish policy towards Ukraine is shaped by the Americans
The new Ukrainian President will not be as submissive towards the United States as President Poroshenko, so the US-Ukraine relations may deteriorate. This situation will cause the automatic worsening of the Polish-Ukrainian relations once Polish authorities realise the American policy towards Ukraine. Thus, relations between Poland and Ukraine will deteriorate not because of historical issues, but because of the complete dependency of Polish foreign policy on the United States.
Recurring pro-Kremlin narrative that the United States is using EU countries to achieve its geopolitical goals and that the EU elites are controlled by America – see examples here and here.
The statement that the United States controls the European and Polish elites is a conspiracy theory. Poland is a sovereign state, which shapes its own foreign and domestic policies - moreover, being a member of NATO and the EU, Poland is able to impact the formation of common foreign policies of these unions. See other examples of disinformation about Polish-American relations here.