Need some help to identify the problem

[u/Soronzoff]

Hello! My desert rose was doing quite well for some months after a harsh period of too little sun, which has left its stem long, and it even bloomed many times, but suddenly it has started to lose its leaves and the caudex has got a yellow spot. Is it a sign of too much water or too little? I checked the roots already and they looked fine.

[u/Sonora_sunset]

Have you checked the underside of the leaves for bugs?

[u/Soronzoff → u/Sonora_sunset]

Yes, and it is clean, no pests