I've very occasionally experience similar with a manual box when on a hill with the 1000kg caravan attached.
The hill hodl / electric park (hand) brake are inter twined with stubbornness.
Often when on the level you engage gear, lift the clutch. press the accelerator and the EPB does not wan't to release. Being impatient you dip the clutch are try again. If you really put some drive on the EPB will eventaully release.
I don't like the "put some drive on" due to wearing the clutch out.
My general 1st solution is to:
o Go into neutral and press the brake pedal a couple of times and try again
Failing that:
o Press the brake pedal and manually release the EPB and then apply again
Failing that:
o Try normal method but in the opposite drive direction
Once or twice I've had to do a 'traditional' manual hand brake release where you pick up the revs and lift the clutch pedal timing the bite / hold and release the EPB. The trouble with this is that you have NO feel to where the bite / hold / release is and the EPB has no variable braking force. Doing that on a hill with a caravan attached is very scary as the EPB can take a full second to full engage if you start to roll. Normally a quick increase in revs & clutch drive will recover the roll but even then it is a bit of a lottery. Stalling is even worse.
ALWAYS when this happens keep you finger ready on the EPB and be prepare to rappidly apply the foot brake.
As you have an automatic then you could try the following.
o Apply the footbreak with your left foot
o Manually release the EPB
o Hold on footbrake and apply some revs
o Feather the footbrake and revs like a traditional hill start with a manual handbrake
Some technical info from the 500X eLearn/KeyLearn
EPB (Electronic Park Brake)
A button activates and deactivate the parking brake, thus eliminating the conventional system for
engaging the parking brake.
The button for the parking brake is located in the central tunnel.
The parking brake function is carried out by the ABS module.
Details below:
The system uses the switch on the central tunnel and two electromechanical actuators, each
installed on a rear brake caliper.
If the vehicle is in motion, pull up and hold the button to engage the parking brake for any
eventuality. The system will operate by increasing the hydraulic pressure.
If the vehicle is stationary, it is only necessary to pull the button upwards once to engage the
parking brake. To release the parking brake, press the brake pedal and press the parking
brake button downwards.
The Drive Away Release function automatically releases the electric parking brake if the seat
belt is fastened, a gear is engaged and the accelerator is pressed in order to move the
vehicle.
The Safe Hold function, when the vehicle speed is lower than 5 km/h, but not in Parking, and
the driver detection algorithm determines that the user is about to exit the vehicle, causes the
EPB to apply the parking brake to stop the vehicle safely.
The Auto Apply function, when the vehicle speed is lower than approximately 3 km/h and the
automatic transmission is set to parking, causes the EPM to apply the parking brake
automatically. With manual gearbox, the parking brake will engage automatically when the
ignition switch is set to OFF.
The status of the EPB functions can be configured in the dedicated Uconnect system menu.