In this case, you might have received bonuses in the original account and the receiving account (of the transferred fund) is not applicable to the bonus promotion.
When you internally transfer funds, the bonus amount will be transferred as well according to the amount.
But if the receiving account is not applicable to the bonus, the bonus amount will be cancelled.
If that is not the reason, you may contact XM support desk and inquire about this.
You are also recommended to refer to XM’s Terms and Conditions for more details.