It wouldn’t be a signal issue. You are probably bumping up against a limit in the SDK. What is the error message that you are getting? See this post for known limits:
Your first waypoint should be placed relatively close to your launch location because all configured waypoint heights will be affected by any difference in height between the launch location and the ground elevation under waypoint 1.
Your Mini 2 depends on a constant connection between the drone and the controller to execute waypoint missions. If the connection is lost the “Signal Lost Behavior” procedure should be triggered. Check to see what you have that configured to be.