Is this a Fidelity NetBenefits account? They provide incorrect balances in Simple mode.
As far as I know, only Fidelity Netbenefits has the problem with Simple mode.
As long as it is not a Fidelity Netbenefits account, Simple investing mode should work for you. It hides the Investing Transaction list and stops downloading the detailed transactions. It just keeps track of how many shares of each security are in the account, and how much cash. With this information and the share prices, it computes your balance. You can still add cash and take distributions.
If the account set up for downloading, it only downloads the necessary information. If the account is offline, you can enter the share quantiries from your monthly statements.
Because Quicken does not track the detailed transactions in Simple mode, performace measures like Average Annual Return will no longer work for that account. Also it can't keep track of dividends or capital gains and losses, but these don't matter in a 401(k) account.