The issue of the data command resetting creature AI.

For example, a skeleton holding a bow, when it has aggression toward a player, normally it would shoot arrows at the player at intervals. However, if any data command is used to modify its data—such as repeatedly executing data modify entity @n[type=skeleton] Fire set value 0—it can cause the skeleton to stop shooting arrows altogether. It may even only follow the player without performing the bow-drawing animation.

As far as I know, other creatures are also affected by the data command to varying degrees, but the specific effects differ. However, the skeleton issue is the most severe.