If you have problems with extremely low throughput in Windows, it may be due to problems with newer versions of the TAP adapter. If that is the case, you can try the following:
1. Open the Device manager
2. Find Network adapters in the list
3. Find TAP-Windows Adapter V9
4. Right click on TAP-Windows Adapter V9 and select Uninstall device
5. Check the option Delete the driver software for this device and then click Uninstall device
6. Download and install the following file: https://swupdate.openvpn.org/community/releases/tap-windows-9.9.2_3.exe