Most likely this was caused by short climbs, which the crew chose to fly in the standard way, ie full thrust with pitch adjusted for speed.
In this way, the thrust will go to max to start the climb, shortly after which the required level is reached, and the thrust goes back to a level flight setting. Then the next climb instruction is received, and it goes to full thrust again to climb, and so on.
This is why some pilots will choose to make short climbs with a set vertical speed, so that the thrust changes are limited.