Used to introduce a specific worry or point of doubt about a plan or situation.
“What concerns me is that we haven't heard back from the supplier yet.”
“What concerns me is how we'll manage if it rains during the outdoor event.”
This phrase flags a personal concern rather than a plain fact, which helps you tell opinions apart from problem statements in CELPIP Listening. Expect the speaker to follow it with a reason for hesitation, which often becomes the basis of a 'why is the speaker worried' question.
Synonyms: what worries me is, my concern is, I'm concerned that