Instructional feedback has the power to enhance learning. However, learners do not always feel satisfied with their feedback experience. Simultaneously, little attention has been paid on investigating how feedback is implemented in online competency-based learning (CBL). CBL is an approach under which learning activities are organized in a non-linear manner to help learners achieve pre-defined competencies. This study applied a multiple case study method, and 17,266 pieces of the coded feedback text, given by instructors for three learning tasks from a blended undergraduate course, were analyzed. The results showed that instructors implemented 11 types of feedback. Feedback that was used to give praise was less effective, but was frequently used. Regulative feedback and emotional feedback can be very effective, but they were actually rarely used. Feedback for diagnosis, suggesting improvements, and praise was frequently and consistently used across tasks with different complexity. In contrast, feedback used for complementary teaching and time management, as well as emotional feedback were rarely used. Based on the obtained findings, the potential causes and suggestions for improving feedback implementation were discussed.