I've experienced the same problem sometimes when internet connection is quite bad . That no data message simply means that your wallet has no fully and successfully synced to the Blockchain and as a result you are not getting the most recent data associated with your wallet.
This is wrong.
Since OP can see the transactions, the wallet is synced.
Take note the blockchain doesn't contain the fiat value of coins. Electrum gets the fiat value of bitcoin at different time from some third parties and then calculate the value of coins itself.
Changing the source of fiat value (as mentioned by Mitchell) should solve the problem.
BTW: Is the Euro value calculated for the time the Bitcoin transaction was performed (in the past) ?
Yes. History rates do not show, same problem in USD.
Electrum displayed the fiat value of the transaction at the time they were made.