Essentially, in a function or command block, execute store does not visually update the entity. This seems to be a server side issue, as if you update the rotation it seems to rotate for a split second and then it changes back.

Example:
execute store success entity @e[type=armor_stand,limit=1] Rotation[0] float 87 if entity @s

Note this command works when the player runs it but not when a function or command block does
Execute store block doesn’t work no matter what