Difficult to accept; unpalatable.
Difficult or impossible to digest.
Anything that is difficult to digest.
Difficult to overcome, solve, or decide.
Contributing (especially if subtly) to discrimination (such as racism, sexism, homophobia, transphobia, or ageism).
Not settled, uncertain, of uncertain outcome; debatable, questionable, open to doubt.
a problematic analysis
A problem or difficulty in a particular field of study.