I would review the troubleshooting options on this page: Troubleshooting Scanning Issues
This option for Device Tester should also prove helpful to track down the cause of scanning issues. In our case, the issue was some ports not being opened that are required by Lansweeper and the relay server in order to pull data from those devices and insert directly into your Lansweeper server.
Alternatively, I would check into IT Agent, which we are currently using now, to bypass your relay server if you are using Lansweeper Sites. This will ensure that devices are returning scans for remote devices and bypass the need to ensure ports are properly open, eliminating the need for a transfer to and from the relay.
IT Agent FAQs
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Union Home Mortgage's "Lansweeper Guy"
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