This is the reason why e.g. you can't import a WIF key to an already created Electrum
HD wallet. You can only sweep a WIF key in such cases.
I don't get it why Electrum won't accept a single WIF key to import. I am using Electrum until now not latest one but it still accepting WIF key. You don't need to import it on the currentHD wallet but you can create a new wallet and import the WIF key.
That is what Cricktor also meant. You can import WIF private key into Electrum, bit that is when you have not created HD wallet on it. If you create HD wallet on it, you will only be able to sweep. Or just create another Electrum wallet to import the private key instead.