The winning chances given are estimates of cubeless winning chances. Estimates can be wrong. Total cubeless winning chances include estimates of how games might have ended if played to the end after Double/Pass. You don't give the position, but it's a pass already. If you double now, you get an evaluation of your winning chances. If you don't double now, you'll be doubling next roll often, and these doubles will again be double/pass. Perhaps XG is slightly underestimating your winning chances in some or all of those double/pass situations.
The redouble/take percent is probably more accurate, but again you keep in mind that it is an estimate of cubeless winning chances. In the following position:
The score is 0-0/5. Blue on roll.
| gnubg | 37 | ||
|---|---|---|---|
                  | |||
| Blue | 33 | ||
| Position ID: e3sBAIAHAAAEAA Match ID: UQmgAAAAAAAE | |||
At 0-0/5 holding a 2-cube, Gnubg says No Double = 79.37%, Double/Take = 79.53%. Your actual cubeless winning chances are 79.54% +- 0.08%. But your cubeful winning chances if you don't double now are probably about 85% (since you will win a lot of games by doubling next roll), and your cubeful winning chances if you double now are probably about 79%, since you will lose some games on a redouble/pass to 8.