See the Errata sheet for your device to see the complete description of this errata and affected products:
CP2102N revision A01
Additional Notes Regarding the Failure Mode
The CP2102N uses the incorrect byte of the SERIAL_HANDFLOW structure (https://msdn.microsoft.com/en-us/library/windows/hardware/jj680685(v=vs.85).aspx) to control the RTS signal. Instead of looking at the first byte of FlowReplace, the device is reading the first byte of the XonLimit and interpreting that as the first byte of FlowReplace.
Applications written in .NET set the Xon/Xoff limits to 160, equal to 0xA0, which the CP2102N interprets as hardware flow control, and so it returns an error when manually setting RTS.
For .NET applications, it is possible to create a software workaround for this issue by setting the XON/XOFF limits to 0x00. Because of additional .NET limitations, the workaround also has to enable hardware flow control, enable the port, then switch to none. These changes enable the CP2102N to properly set or clear the RTS signal manually.
The attached source file contains a software workaround for .NET applications.