BeePrint work with FLSun QQs-Pro stock firmware but not with marilin

Hi, first of all, thank you for your wonderful work. I followed the entire preparation procedure on my FLSun QQs-Pro with the stock firmware. after doing the first tests, everything works great. I tried to redo the same procedure with the marlin 2.1.2 firmware. The web interface works normally, but the printer appears disconnected. I made several attempts but couldn't solve it. Can you give me some suggestions to solve it?