Evidence: REFUSED (threshold). collapsed HTTP 500 returned 0 row(s) against a RowLimit of 100, labels [], grouping markers [], first row null; expanded HTTP 500 returned 0 row(s); the same query with no <GroupBy> returned HTTP 200 with 100 row(s); collapsed body {"odata.error":{"code":"-2147024860, Microsoft.SharePoint.SPQueryThrottledException","message":{"lang":"en-US","value":"The attempted operation is prohibited because it exceeds the list view threshold."}}}. The fixture gives LVChoice four values, ["Alpha","Beta","Gamma","Delta"], over 5500 file(s). A group-by is not honoured here on a plain single-value column, so nothing below can attribute an unhonoured group-by to LVCalc being calculated.