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.
What wallet version do you use?
My current electrum version: 4.5.8