could you take some pictures with a microscope? Dorsal view and ventral view, also detail picture of the ventral plates. Mesostigmata, too many setae on the dorsal shield to be a Phytoseiidae.
From the figure my guess is that it might be the mesostigmate mite Kleemannia plumosus (Oudemans). I know it from decaying hay and cereals. You may read about this species in Hughes M 1976. The mites of stored food and houses page 337.
General shape of ameroseiids. More pictures needed for both sides. Away from Phytoseiidae. For your knowledge, some researchers use subgenera (Kleemania & Ameroseius) under the genus Ameroseius based on the number and position of the preanal setae ventrally, while other do not (all species in one genus Ameroseius). Good luck!