The floating object in the humpback whale’s path at first looked like an ocean sunfish, which are roundish and can often be seen lazily floating on the water’s surface.

https://www.pvnews.com/news/does-a-plastic-bag-stuck-on-whale-s-mouth-indicate-more-ocean-trash/article_cc1d44b6-5b4b-11eb-a850-dffd0f5b7f45.html