I just installed yesterday electrum and there was a default wallet, and asked me the password so I did and showed me my transactions of my BTC wallet.
I think I installed it some years ago maybe and the default wallet remained in my roaming folder I guess.
Btw I downloaded it from official electrum website . Then it showed me my balance and couldn't believe my eyes .
So you don't import anything then? No seed/private key? Did you verify that it's the real Electrum app? Have you verified if it was the same wallet you created with Bitcoin Core? Why don't you download Bitcoin Core again and try to check your wallet with it? Have you verified it those address belongs to you by checking through the console as suggested above? I think it will be easier to understand if you explain these details further. I believe some suggestions above are quite helpful so try to check them out.