I have the same problem. Adding and saving a new token, which is not in the list of tokens in the MEW wallet, it appears, but after re-entering the wallet, everything has to be done on a new one.
If we add a new custom token to our MyEtherWallet wallet, a minus sign appears in the circle next to the token symbol. If you accidentally click on it, the user token again will no longer be visible. Coins will be in your wallet, but you will need to repeat the operation again with the addition of a new user token. In order to check if there are tokens in the wallet, it is better to use the function etherscan.io.