Occasionally, we don't receive all your data for a particular period and if this happens you will see a question mark where your usage would normally be shown. For example, your meter may be unable to send its data to us because of a glitch with the network. This is usually temporary and we typically get the missing data within a couple of days.
Usually, this relates to a transmission problem not a data problem and you meter is still measuring your power use perfectly. It's very unlikely to affect your bill.