I followed all the possible advices:
1 - Good drainage holes
2 - Fast-draining potting mix, be it 50/50 coco-perlite, added coarse tuffa or river sand, or just using pure Perlite
3 - Let it dry for a few days before the next irrigation
4 - Keeping the center dry
5 - Looking for heat-tolerant and direct-sun tolerant species
The problem: Echeverias may rot suddenly without warning. It does not necessarily start at the root.
Exceptions: Echeverias in the garden have endured winter rains, hail and scorching summer. One species was more sensitive to rot, yet still performed better than the potted ones. They needed less water and endured wetting the center of the crown by rain or irrigation.
So what I may be doing wrong with my potted one? I live in zone 11. My climate is Mediterranean. The summers are hot and humid but have no rain from June to October.