One column will not sort in grid.

I have a Tempo report that contains 15 grids, 14 of which will sort the data on clicking the column headers. This one does not. What am I doing wrong?
rule!APN_uiSectionOneColumn(label: "Projects Launching in the Next 30 Days", contents: {

with(
projects: rule!GET_NEXT_30_DAYS(
'type!PagingInfo'(
startIndex: 1,
batchSize: -1
)
),
if(rule!APN_isEmpty(projects), {},
load(
gridPagingInfo: topaginginfo(1,-1),

rule!APN_uiPagingGrid(
           label:"",
columns:{
rule!APN_uiGridTextColumn(
label: "Projected Launch Date",
data: projects.data.projectedLaunchDate,
field: "projectedLaunchDate"
),
rule!APN_uiGridTextColumn(
label: "Category",
data: projects.data.category,
field: "category"
),
rule!APN_uiGridTextColumn(
label: "Product",
data: projects.data.site,
field: "site"
),
                     rule!A...

OriginalPostID-85350

OriginalPostID-85350