Field not showing up in one environment only

A general question, but could you give more info on the rule used specifically for that column?

Is it plug-in related? Built using OOTB functionality? etc.?

Maybe with this information, either another practitioner or myself can follow up more efficiently.

I think it might be something related to the access on report to the groups which are trying to access that column or it can be related to access on the column as well. But yes, you can either share the code so that we can take a look and provide you some insight.

Here is the code (in a few parts):
The column:
a!gridTextColumn(
label: "Current Assignment",
field: "currentAssignment",
data: a!applyComponents(rule!PD_getFirstProcessAssignee(_), index(ri!datasubset.data, "opportunityId", {}))
),
The rule called in the applyComponents():
load(
local!queryResult: a!queryProcessAnalytics(
report: cons!LAM_TASK_REPORT_FOR_PROCESS,
contextProcessIds: index(
rule!LAM_getActiveTaskTrackingEventByObjectTypeAndId(
ri!opportunityId,
cons!LAM_EVENT_TYPE_TASK_TRACKING
),
"processId",
{}
),
query: a!query(
logicalExpression: a!queryLogicalExpression(
operator: "AND",
filters: {
a!queryFilter(field: "c1", operator: "in", value: enumerate(2))
}
),
pagingInfo: a!pagingInfo(startIndex: 1, batchSize: 1)
)
).data,
if(
rule!APN_isBlank(local!queryResult),
{},
rule!LAM_RecordsTaskDisplayUserOrGroupNames(local!queryResult.c5, 1)
)
)

Both the expression rule and the column are working correctly in the Production environment, so I am having trouble diagnosing the problem since I haven't been able to find the cause

This is just my initial guess Kyle, but I think the difference lies in the fact that you're using a!queryProcessAnalytics(), which derives its information from the context of the environment. In other words, the processes between Dev/Test/Production environments are probably going to differ (unless the info they all query is very consistent/unchanging) so I don't think, code-wise, there's anything wrong with what you've shown especially considering this has worked successfully for you in both Dev & Test.

For assurance, you can verify if your constants are actually holding values & are not just empty from the import which shouldn't be the case.

I may have misunderstood with the 1st portion of my comment, so ignore if needed, but the 2nd portion, you may want to also double check if there's any reason you need to change the column that you're referring to (c1, c5, etc...) in your code for some reason (maybe it was changed accidentally at some point??).

I can confirm that both cons!LAM_EVENT_TYPE_TASK_TRACKING and cons!LAM_TASK_REPORT_FOR_PROCESS have the correct values in them in the Production Environment.
The code itself works in Production as well; I can feed the Expression Rule an Opportunity ID and it will return the correct assignee and the grid itself is showing all the correct assignees. The only place it isn't working is in the report, in tempo, in the production environment.

Does the code not work for you in tempo or does it not work for a basic user in tempo?

It does not work for me in tempo

My next debug step would be creating a report only I can see and just spit out the results of the rules to see if it's an issue with the grid or with the rules themselves.