Several species such as Dioscorea, Massonia and Veltheimia grow in winter.
During this period they should be above 15 °C and watered regularly.
Waterlogging and cold feet should be avoided at all costs.
In summer these species lose their foliage, this is natural and there is no need to worry.
The bulb/caudex survives this dormant period without watering and sprouts again in late summer/autumn.