I had a view that used "Group By" to sort on a "Status" column that had several values. The list had only 600 records. The "Group By" showed values but you couldn't see the records for one of the values and there were only 4 items with that particular "Status". I changed the Style to "Shaded" from "Default" and it worked again. Tried to google to figure out why the change worked but couldn't find anything that might have explained it. Thanks in advance for any background as to why this fixed it.
Status: Request Completed (509)
<Could see all 509 items>
Status: Releases (87)
<Could see all 87 items>
Status: Under Review (4)
<Could NOT see any items and when tried to expand nothing happened>