Did it confirm? Can you try to restore your wallet from its mnemonic phrase and see if that helps witb anything (if restarting it hasn't already worked).
That is true, this will be a good idea.
You can't delete an unconfirmed transaction from the blockchain, it just gets deleted from your wallet. There's a chance the person that sent you the funds double spent them and replaced the destination of the funds.
@TJXMB, this is very true.
If you have just downloaded the wallet, and someone sent you bitcoin, the unconfirmed transaction will appear on your Electrum wallet balance. It is possible the sender to double-spend the unconfirmed transaction with a higher fee in a way he will send back the coin into another address which can even be his. If so, I guess the transaction will no more appear on the history tab.
This will also occur regardless of it being a newly downloaded wallet or not. I just used new downloaded wallet to explained it because no transaction will be found in the history no more as it is the first transaction (which was later double-spent). But for old wallet, the history is intact, only the unconfirmed transaction that was double-spent wod also be the one not seen again.