Update:
I've repotted the plant with my camera ready but not much root was to be photographed as the current pot was still more than sufficiently big. However, the soil at the bottom was bone dry, even though I thought I watered it thoroughly. So I now transferred it to a bigger pot, with better soil, through which I mixed some dry slow-release fertilizer as well. Then I watered it until all of the soil was wet, and now it is sitting comfortably in the sun
Hopefully this triggers some healthy new leaf growth!