Answered by Shaykh Faraz Rabbani
Can one wear khuff on one foot only and wipe over it while doing regular wudu on the other foot? This is just a question about validity of the wudu, not really touching on the fact that it is rather strange to wear the khuff on one foot alone.
Assalamu alaikum wa rahmatullah,
No, it is not valid to wipe on footgear on one foot and to wash the other. [Zayla`i, Tabyin; Shurunbulali, Maraqi al-Falah]
And Allah alone gives success.
Faraz Rabbani
ولا تجتمع الوظيفتان في الرجلين (تبيين الحقائق شرح الكنز)
(ولا يجمع بينهما ) الغسل مع المسح على الخف في إحدى الرجلين