The store (like most time-dependent facets of the game) relies on an accurate and stable clock in the device. If the clock is deliberately or inadvertently changed, the store's restocking schedule is disrupted, especially if the clock is moved backwards in time. At this time, there is not anything you can do to correct that situation when it happens (other than waiting to see if the store starts restocking again on its own), although we are looking at the issue.