Sound issue on R36S clone after installing K36S Stock EmuELEC 4.7 firmware

Hello everyone, I have an R36S clone and I recently formatted the SD card because it was damaged. I installed the K36S Stock firmware (EmuELEC 4.7) https://handhelds.miraheze.org/wiki/R36S_Clones#Custom_Firmware_for_the_EmuELEC_Clone,
and although the ROMs display fine, I have a problem with the sound: when I connect headphones, it plays without problems, but when I disconnect them, the sound from the speaker returns only for a few seconds before turning off .

Has anyone had this problem or know how to fix it? Thanks in advance!