Hanafi
The sources give no view for it here.
القضاء على المفطر في التطوع
هل يجب القضاء على من أفطر في صيام التطوع؟
Each school’s answer
In our wordsHanafi
Not stated in the sources
Maliki
Not stated in the sources
Shafi'i
Not stated in the sources
Hanbali
Not stated in the sources
The texts
ب - فِي تَرَتُّبِ الْقَضَاءِ وَغَيْرِهِ: ٧ - يَجِبُ الْقَضَاءُ عَلَى مَنْ أَفْطَرَ فِي صِيَامٍ وَاجِبٍ وَهَذَا بِاتِّفَاقٍ. وَفِي صِيَامِ التَّطَوُّعِ خِلاَفٌ. وَقَدْ يَكُونُ مَعَ الْقَضَاءِ فِدْيَةٌ أَوْ كَفَّارَةٌ. وَفِي ذَلِكَ تَفْصِيلٌ يُنْظَرُ فِي مَوْضِعِهِ.
«الموسوعة الفقهية الكويتية» (Kuwait) entry «إفطار» vol. 5 p. 299
From the schools’ own books
Maliki
The sources give no view for it here.
Shafi'i
The sources give no view for it here.
Hanbali
The sources give no view for it here.
What is «in our words» is our standard wording; the books’ texts stay as they are.