hi, is urs a manual or auto, did u put the hand brake in service mode plse
if it doesn’t go on it normally means it’s needs adjusting , so that when u put the EPB it has enough travel to lock on
maybe ur shoes are too tight to the inside of ur disc, , so when u apply the EPB it hasn’t got enough travel to hit the sensor inside the EPB ecu so goes back off again , but screeches as the motor strains trying to apply them because there’s not enough slack in the cables
did u adjust the shoes through the disc hole or just fitted the discs
when bleeding the brake system if u empty the ABS unit u then need a diagnostic machine to open it to allow it to be fully cleared of air, but i imagine not much came out when u removed the caliper
just for a useless bit of info , u can also use a diagnostic reader to set the EPB shoes into dismount mode which allows u to get the shoes on and off easier,
hope that makes sense, lol ,
PS, video of what’s inside the EPB module