ccxt: Problems with fetchBalances() for Three Out of Five Exchanges

I’m attempting to use five exchanges right now, all of which work fine except for Poloniex, Bitfinex, and Kraken when it comes to fetchBalances(). I get these errors:

poloniex: Error: poloniex POST https://poloniex.com/tradingApi 422 Unprocessable Entity bitfinex: Error: bitfinex POST https://api.bitfinex.com/v1/balances 400 Bad Request Possible reasons: invalid API keys, market down or offline, on maintenance, DDoS protection, rate-limiting in effect kraken: TypeError: Cannot convert undefined or null to object

They all return loadProducts() just fine, and I know have the correct credentials. Is there something special about these exchanges I might be missing when it comes to fetching balances? So far, GDAX and Bitstamp work fine.