https://www.polygon.com/2018/4/13/17235268/destiny-2-warmind-power-level-changes

In a weekly update from Bungie, Destiny 2 combatants design lead Tomonori Kinoshita dropped some interesting news about changes to the game’s difficulty. Starting in season three, which launches May 8 alongside the Warmind expansion, enemies will be getting a boost in potential power.

Players who are under-leveled will now have a much harder time when facing down enemies who are higher power level than they are. If the threshold is too wide, over 50 power, then they will become immune to all damage. Destiny players should be familiar with this system.