When I enter in this command:
/summon Item ~ ~1 ~ {Item:{id:"minecraft:wheat",Count:1b}}
The items gets summoned and stays there, but when I enter this command
summon Item 177 97 -142 {Item:{id:"minecraft:wheat",Count:1b}}
The item appears and instantly disappears. From this small test, I have found that adding the coords breaks it (177 97 -142) Also take note that when I walk to the location that I summoned it, I still cannot pick it up, thus it is not a graphical glitch.
I have provided screenshots below, you will see the item behind the villager in the background.