Occasional null balances returned on `getBalance` balance call.

[danjm]

Symptom of this bug described in #5723

Network requests for getBalance (https://web3js.readthedocs.io/en/1.0/web3-eth.html#getbalance) to infura seem to arbitrarily return null for the balance

Here are four such network requests and the responses, made on four successive block updates:

Request
GET https://api.infura.io/v1/jsonrpc/mainnet/eth_getBalance?params=%5B%220xbfc4bf9c3b454eb7fb9e4d1b95e4c1f53e5330bf%22%2C%220x6767f0%22%5D

Response
Status: 200
Payload: {"jsonrpc":"2.0","id":0,"result":"0x1d2d8f25e458"}

----
Request
GET https://api.infura.io/v1/jsonrpc/mainnet/eth_getBalance?params=%5B%220xbfc4bf9c3b454eb7fb9e4d1b95e4c1f53e5330bf%22%2C%220x6767f2%22%5D

Response
Status: 200
Payload: {"jsonrpc":"2.0","id":0,"result":null}

----
Request
GET https://api.infura.io/v1/jsonrpc/mainnet/eth_getBalance?params=%5B%220xbfc4bf9c3b454eb7fb9e4d1b95e4c1f53e5330bf%22%2C%220x6767f6%22%5D

Response
Status: 200
Payload: {"jsonrpc":"2.0","id":0,"result":"0x1d2d8f25e458"}

----
Request
GET https://api.infura.io/v1/jsonrpc/mainnet/eth_getBalance?params=%5B%220xbfc4bf9c3b454eb7fb9e4d1b95e4c1f53e5330bf%22%2C%220x6767f7%22%5D

Response
Status: 200
Payload: {"jsonrpc":"2.0","id":0,"result":null}

These requests are ultimately triggered by the account-tracker on block updates. When they are sent, a request is sent for each of the currently added accounts. So one you can observe them in your console in groups.

One strange occurrence is that in any given group, it is possible for 1, 2, 3 or 0 of the responses to have a null balance.

[W3stside]

Seconding that this happens for us. Exact same call. We have also seen certain Contract.sol calls returning imposisble values. In this case a [0, 0] (in BigNumber) when such case is impossible.

EDIT: For more clarity: in the above function, the explicit return is stated as (uint num, uint den)

[Gudahtt]

Closing, as we haven't had reports of this in a long time. Please open a new issue if you see this again!