I have a similar problem. The solenoid opens but then there is not enough voltage to keep it open. The output voltage on start is 24VAC, then it goes rapidly down to 6,5VAC. This is not sufficient.
I’m wondering if it is a power supply issue (Output 24VAC, 1500mA – not sufficient power) or if there is the possibility to change the power output parameters in the software, increasing the transient duration or increasing the 6,5 to something like 9VAC.