How are you exporting the private key? Did you run dumpprivkey YOUR_ADDRESS?

Can you try creating a new Bitcoin Core wallet, and then importing that private key into the new wallet using importprivkey, and see if the new wallet shows a different address?

Alternatively it's possible that in Electrum you pasted the private key without putting p2wpkh: in front of it? If you don't do that then you might generate an address starting with a "1" or "3" instead of native segwit's bc1.