The following idea came out of the "bug" reported here:
https://community.simplifimoney.com/discussion/comment/7716In order to avoid the scenario outlined in the bug, one solution would be to allow individual goal contributions to be ignored from the spending plan.
This would be useful, for instance, if you are contributing funds that were just "released" from another goal. In that scenario, it is reasonable to assume that the contribution should not count against the spending plan as it is not coming from the current month's income.