Current Account Balance Error
Currently, as of July 26, there is an error in Metamask when reading user account balance. What the user will see, when they open the Metamask Extension, is the user balance section and the user order section goes into infinite load without an apparent error.
Should this error appear, simply disable and re-enable your Metamask Wallet.
Basically what happens is the user balance and user order sections won't show and the spinner constantly spins. This is not an exchange problem and your funds aren't lost. This is an error in Metamask when fetching account data. It is stuck fetching data and never fetches it, so it hangs indefinitely.
This is not an existential problem and Metamask is currently developing a patch.
Currently waiting on "formal retrospective" from Metamask team. See more details on this Cointelegraph article. Stay tuned.