Take off power lost

Hello,

During last flights take offs (not in all of them) I suffered engine power lost, maximun developed was 4.700 rpm (from 5.200 normal setting). Situation is from ralenti to full power (also happent in a go around). After a little while flying power resume to normal.

Engine is a new 912ULS with only 85 hours.

Any advice to check???

Thank you.

Andres