The refrigerator accidentally got sleet wheat grain from dupes but there is no sleet wheat grain in element filter for refrigerator.
I can't find the way to get back the sleet wheat grain in it, toggle all element from checked to unchecked and use the 'empty storage' doesn't work, dupes ignored. But dupes still can take it out if there is any building needs to use sleet wheat grain such as cooking station.
** Updated **
After this bug occurred, all refrigerators can store sleet wheat grain even not selected to store anything.