1
general::
Phrase(s): crop up
to appear without warning; to happen suddenly; [for something] to begin to reveal itself in the open. • Some new problems cropped up at the last minute.
McGrawhill's American Idioms And Phrasal Verbs
2
general::
Appear unexpectedly or occasionally, as in One theory that crops up periodically is the influence of sunspots on stock prices, or We hope new talent will crop up in the next freshman class. [Mid-1800s]
American Heritage Idioms