After 6/3*, your bot is doubling with Jacoby, and not doubling without Jacoby -- right?
Correct. Without Jacoby XG 3-ply errors by not doubling after 6/3*.
In my two rollouts XG correctly doubles after the hitting play.

              
 
              
 | | White is Player 2
score: 0 pip: 109 | Money session Jacoby Beaver | pip: 106 score: 0
Blue is Player 1 | |
| XGID=-BBa--D-Cb---D---aabbbbb--:0:0:1:21:0:0:3:0:10 |
| Blue to play 21 |
| 1. | Rollout1 | 8/6 2/1 | eq: -0,211 |
| Player: Opponent: | 44,57% (G:1,89% B:0,03%) 55,43% (G:10,87% B:0,15%) | Conf: ± 0,013 (-0,224...-0,198) Duration: 32 minutes 26 seconds |
|
| 2. | Rollout1 | 6/3* | eq: -0,263 (-0,052) |
| Player: Opponent: | 43,42% (G:3,23% B:0,06%) 56,58% (G:19,95% B:0,12%) | Conf: ± 0,017 (-0,280...-0,246) Duration: 42 minutes 41 seconds |
|
| |
1 1296 Games rolled with Variance Reduction. Rolled for both No double and Double Dice Seed: 36095669 Moves and cube decisions: 3 ply
|
eXtreme Gammon Version: 1.21

              
 
              
 | | White is Player 2
score: 0 pip: 109 | Money session Beaver | pip: 106 score: 0
Blue is Player 1 | |
| XGID=-BBa--D-Cb---D---aabbbbb--:0:0:1:21:0:0:2:0:10 |
| Blue to play 21 |
| 1. | Rollout1 | 8/6 2/1 | eq: -0,230 |
| Player: Opponent: | 44,52% (G:1,92% B:0,03%) 55,48% (G:10,90% B:0,13%) | Conf: ± 0,012 (-0,242...-0,218) Duration: 35 minutes 06 seconds |
|
| 2. | Rollout1 | 6/3* | eq: -0,270 (-0,040) |
| Player: Opponent: | 43,23% (G:3,21% B:0,08%) 56,77% (G:20,00% B:0,16%) | Conf: ± 0,017 (-0,287...-0,253) Duration: 45 minutes 12 seconds |
|
| |
1 1296 Games rolled with Variance Reduction. Rolled for both No double and Double Dice Seed: 36095669 Moves and cube decisions: 3 ply
|
eXtreme Gammon Version: 1.21