Some users have reported problems connecting to their UniFi controllers using PCs and Laptops.
The error is either "No network available", or the connection drops / disconnects occasionally.
We found this article which might be useful in troubleshooting the issue:
If you experience this issue, try this fix:
Make sure Auto-Optimize Network and High Performance Devices are disabled.
Settings > Site > Auto-Optimize Network
Settings > Wireless Networks > SSID > Advanced Options > High Performance Devices
Also, could you post your system config?
Settings > Maintenance > Support Info > Show System Config