The preview results are formed by multiple snapshots put together, if the loading speed is too slow, improving the internet connection might help.
Go to software: Beam Studio > Menu > Machines >Test Network Settings.
Fill in the Target device IP Address column with the machine IP address.
Press Start and the test will start running.
If the average response time is over 100ms, try reducing the distance between the machine and the router or mobile hotspot, or change to a wired connection.
If none of the steps above work, please refer to this link for troubleshooting-https://support.flux3dp.com/hc/en-us/articles/360001111355-Camera-Preview-Timeout-or-Failed-to-Connect