To successfully deploy Splashtop to a device, it must be enabled for all policies the device is assigned to.
In other words, Splashtop must be enabled per policy where you'd like to use the tool.
Disabling the integration in a Child policy will override the state of the Parent policy. Thus, enabling the integration at the Parent level does not automatically enable it in Child policies.
Child policies have Splashtop disabled by default - it must be enabled for each individual Child policy.