The messages and bars on the Where’s My Refund? tool change all of the time; and sometimes the same message is displayed continuously, or the bars disappear entirely (they may return later). The disappearance of the bars, as a stand-alone action, signifies nothing important at all. The behavior that you observe is more likely an indicator that your tax return (and refund) is simply moving through the processing system.
Please in keep in mind that the IRS doesn't always move as fast as taxpayers would like (especially when waiting for a refund). Also taxpayers who report certain items of income (such as self-employment) or certain tax credits (such as dependent care) can experience longer wait times for the IRS to process their original tax return, and ultimately issue a tax refund.
Please see the articles below for more information: