From the IRS:
Why is my refund being held?
Beginning in 2017, if you claim the EITC or ACTC on your tax return, the IRS must hold your refund until Feb. 15. This new law requires the IRS to hold the entire refund — even the portion not associated with the EITC or ACTC. Like previous years, some tax refunds may be held if there are questions about the tax return or the IRS needs more information.
Will I get my refund on Feb. 15?While the IRS will begin to issue EITC/ACTC refunds starting Feb. 15, you should not count on actually seeing your refund until the week of Feb. 27 -- if you chose direct deposit or a debit card and there are no processing issues with your tax return.
Why does it take so long for the funds to show up in my account?It takes additional time for refunds to be processed after leaving the IRS, and for financial institutions to accept and deposit them to bank accounts and products like debit cards. Also many financial institutions do not process payments on weekends or holidays, which can affect when refunds reach taxpayers. For EITC and ACTC filers, the three-day holiday weekend involving President’s Day affects their refund timing.
“Where’s My Refund?” Begins Updating Feb. 16 for EITC and ACTC Filers
By law, the IRS must hold Earned Income Tax Credit or the Additional Child Tax Credit refunds until Feb. 15.Taxpayers will begin to see refunds claiming EITC/ACTC the week of Feb. 27. “Where’s My Refund?” will update for EITC/ACTC refunds beginning Feb. 16, with the vast majority updating by Feb. 18.
https://www.irs.gov/uac/newsroom/avoid-the-rush-use-irsgov-for-quick-answers-to-questions