Electrum will always allow you to add more private keys to that wallet.
If it's another type of wallet, please verify your Electrum's signature to make sure that it's not a fake.
But if the issue is the history and the transactions and balance are somehow fetched correctly;
Check if you've set a "filter" before, a drop-down menu should be displayed above the history, select "All";
if there's none, then it's disabled. Use "Wallet->History->Filter" to re-enable it.
it was a newly created wallet last week to which I did use the import private key.
as for the part you got lost on - sorry, I was importing multiple private keys from core, but they were different formats (1, 3, b) so when I was importing them to Electrum it was using different public addresses than the ones that had transactions so the amounts that involved multiple public addresses were being reflected incorrectly by Electrum.
when I added the part stated by
To import a Legacy address (1...) , p2pkh:
To import a Nested segwit address (3...), p2wpkh-p2sh:
To import a Native segwit address (bc...), p2wpkh:
....
in front of the private keys, it then did bring in the right addresses and the transactions are all reflecting correctly.
i have never encountered this issue and i have imported both addresses (as watch only) and private keys (full wallet capabilities) in Electrum many times and all the history of all addresses show up correctly in the History tab.
are you sure your client is already in full sync with the network? if you had a very large number of transaction history it could take some time for the node you connect to to send back all that history that should then be written to disk. Electrum is also known to be slow when the wallet size becomes big.
i'm curious what the addresses you imported were. for example how many transactions did each of them have? and were these transactions made recently or many years ago?
corrected it by using the method as described by Csmiami