Answer
Check whether a custom Logical Unit or report involved has a name close to Oracle's 30-character object-name limit — in one confirmed case, a custom LU created via an outside/non-standard tool had a 27-character name that, once converted into its corresponding database view/table name (with IFS's standard prefixing/suffixing applied), exceeded the 30-character maximum, causing that view to silently fail to register properly in the dictionary. Shortening the LU's name so the resulting database object name stays within the 30-character limit resolved the issue and allowed Conditional Fields to work normally again.