Particle Argon controlling 12V, using 3.7V LiPo
Your battery and step-up converter are not able to supply enough current for the motor.

To estimate how much current is needed, let's use the worst-case current required by the motor, which is the stall current of 1000mA at 12V. Depending on the load, the normal operating current looks like 100mA to 500mA, but I would expect a brief current close to the stall current when the motor starts.

So, if we need 1000mA at 12V, and we (unrealistically) expect 100% efficiency from the dc-dc converter, then you need 3000mA at 4V into the converter. This exceeds the maximum discharge current of the battery (by 3X) and also exceeds the maximum input current of the dc-dc converter (by over 2X). This is an optimistic estimate. It gets worse as the battery discharges and its voltage gets lower, and it gets worse if the actual efficiency of the dc-dc converter is considered.

So, bottom line, you need a much larger battery and a much more capable dc-dc converter. You might also consider using a separate battery for the actuator so the current surges don't affect the electronics.