In 6.4 there was a switch in the admin orders to turn the discounts on and off, and thus recalculate them when a change is made (items are added or removed).

In 6.5 it is no longer available at this point.
Instead, there is such a switch under the Details tab.

If I deactivate the discount, a message appears that changes should be saved, but after saving and switching to the General tab, the discount is still present.

A discount can then only be deleted manually, because unfortunately it does not automatically adjust to a change.
Afterwards, you have to reactivate a discount in the Details tab.

This is unfortunately a very unfortunate and uncomfortable situation.
Multiple saving, switching pages, turning discount actions on and off, etc.