This is the 5772nd most frequent Japanese word.
なにか
"Something" or "anything."
In this sentence, 'なにか' is used to refer to an unspecified thing that the subject is assumed to be seeking. It expresses the idea of 'something' without specifying what it is.
彼は何かを探しているようです。
He seems to be looking for something.
Here, 'なにか' is used to introduce the possibility of any problems existing, emphasizing the unspecified and indefinite nature of the potential issue.
何か問題があったら教えてください。
If there's any issue, please let me know.
In this example, 'なにか' works to introduce the idea of something unspecified and peculiar that occurred in the past.