2 entries created by using activerecord find_or_initialize_by followed by update_attributes

I am using find_or_initialize_by followed by update_attributes to create new entry else update if entry already exists.

below is the code snippet in Ruby.

StudentResult.find_or_initialize_by(
        :course_id => course_id,
        :student_id => student_id,
        :assessment_id => assignment_id,
        ).update_attributes!(
        :total_score => assignment_total_score,
        :score => assignment_score
)

But I can see there are 2 entries for the same combination of course_id, student_id, assessment_id. This is happening rarely for some records only.

course_id, student_id, assessment_id , total_score, score, created_at , updated_at
7779,156035,29792,30,0,2020-02-06 13:54:30.325446,2020-02-06 13:54:30.325446
7779,156035,29792,30,0,2020-02-06 13:54:30.326769,2020-02-06 13:54:30.326769

Currently I do not have any unique key constraints on table StudentResult. But ideally it should create only 1 entry for course_id, student_id and assessment_id combination. I am skeptical that can this be due to some race conditions or I am missing something in my code.