Is it permissible to combine the fasting of the six days of Shawwal with the fasting of days of vows, knowing that there are still missed days from Ramadan that must be made up?

Whoever has to make up for missed Ramadan fasts, pay expiation (kaffarah), and fulfill a vow (nadhr), should prioritize the make-up fasts, then the expiation, then the vow. It is permissible to fast the six days of Shawwal before the vow fast, unless the vow was for a specific, designated time.