Crossword Genius

Bringing forward time of festival causes problem (6)

Ross

I believe the answer is:

teaser

'problem' is the definition.
(I know that teaser is a type of problem)

I cannot understand how the remainder of the clue works.

(Other definitions for teaser that I've seen before include "Difficult problem concerning Easter" , "one using a backcomb" , "One who pulls someone's leg" , "Hard question" , "Easter (anag) - puzzle" .)

I've seen this clue in The Guardian.
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