Limitations in Trial Version? support confirms that there are no limitations on the number of endpoints you can register with managed remote desktop when in trial mode. Possibly you set the time for one of the customer deployments to something like a day or an hour and it timed out and you'll need to reinstall with a new agent. But it would probably be good for you to let us know exactly what you did to deploy to the customer endpoints including all the options you selected. If you don't want to share that on the public forum you can DM me.