from MACHINE M
and used the alias M in the rest of the query. The report worked fine in KACE and in MySQL Workbench, but no computers were ever being added to that label. Long story short, as soon as I removed the alias and used the actual table name instead, the Smart Label worked.
This doesn't appear to affect table aliases in JOIN clauses; only the FROM clause.
(K1000 6.4 SP3)