Why is there a difference of opinion between vadakalai and thenkalai sects of Sri Vaishnavam? Did these exist from the times of Jagadacharya Sri Ramanuja?

These differences did not exist during Sri Bhashyakarar times.
Notes:
There is a difference in terms of doctrine. The meanings provided by Acarya are interpreted differently by everyone in their way. In course of time, the difference in doctrine had ended up with differences in anushtanam.