This bug has been around for a long time, and there is currently no definitive solution. Although I am not sure what caused it, many people have encountered similar situations.
There are many solution ways, you can try.
1. Back up your wallet, then uninstall your semux wallet, delete all the data, and reinstall it.
2. Quit your VPN, if you don't use VPN, try changing IP.
3. Delete the data about the network connection in the Regedit and restart your computer.
4. Restart the router.
5. Reinstall Window.