The first step is to understand why the robot is not starting. Is this due to the package load failing or timing out? if the second you can simply increase the time allocated for the package to load in Robot Manager in the edit Work Group screen over the assigned package. If the second we'll need the runtime logs to understand the error.
It might be that one of the applications required it is not starting correctly.
Runtime is only sending the ready to work message when the package is fully loaded. this means that if your solution is starting all the adapters it won't sent the event all projects started until this happens. The solution is to increase the package loading time so the expectation from Robot Manager is set to the right value.
If this is not consistently happening and the expectation is that the solution starts quicker than it is actually doing. We need to find the adapter that it is slowing down the startup process to understand why it is slow.