Quest Sync
Quest Sync is a mechanic introduced in Heavensward for the rewards of Quests that employs an automatic level adjust system. Quests that are subject to Quest Sync are denoted with the symbol .
Quests using this system will have their difficulty and 
EXP rewards adjusted to match your current level within the expansion's level range. Heavensward quests will sync from level 50-60, for example, and doing quests at a higher level than the maximum sync will sometimes result in reduced EXP rewards.
Not every side quest uses Quest Sync, but all 
Allied Society Quests do beginning in Heavensward, and so do all 
Side Quests beginning in Shadowbringers areas. If a quest uses sync it will display this message in its quest box:
※Please note that the difficulty of this quest has been synced to your current level.
In Cosmic Exploration, class D, C, B, and critical Stellar Missions are quest synced, scaling the mission difficulty and EXP rewards to the player's current level (up to level 100). However, currency, Cosmic Tool data, and Cosmic Class Points do not scale based on level.
See also
Some quests contain instanced duties. For the mechanic applied during those quests, see Level Sync.