Yes, I forgot to add that, off course, I cleared the flash with Esptool gui v3.6.4, with esptool.py v2.3.1 erase_flash command and I also uploaded a full 4MB file of 0xFFs and a full 4MB file of 0x00s (even with the -no_compress flag). By the way, I guess that should it be a software/firmware/configuration problem, it should behave every time exactly the same, isn't it?