Skip forward to trick 11, from East's perspective.
All South and West have are 6 diamonds between them. There are 20 possible ways these could be arranged.
In 18 of these, returning a heart results in *less* tricks than returning a diamond.
In 2 of these, returning a heart results in the same number of tricks as returning a diamond.
Gib returns a heart. This means it only simulated two of the twenty possibilities.
Even basic robots should do better than that. This needs to be fixed.