This issue could be cause by an SQL timeout error, this can be found in the xcAdmin.log, here is an example of how it may look:
2020-03-10 13:11:33.454 Severity: Error, Switch: TraverseTiming Message: Error setting input parameters in Activity report: 'Execution Timeout Expired. The timeout period elapsed prior to completion of the operation or the server is not responding.' - ' at Axceler.Datalayer.xcDataManager.GetDataTable(String dtName, String connName, String sSQL, Dictionary`2 hshParm, Boolean executeWithSQLParms)
at Axceler.Datalayer.xcDataManager.GetDataTable(String dtName, String connName, String sSQL, Dictionary`2 hshParm)
at Axceler.Core.Logic.Operations.ActivityByUserOperation.#vO(SPSite #1j, DataTable& #yy, List`1 #wO, Dictionary`2 #tz, WebDataManager #tF, String #rO, String #3j, Boolean #sO, String #tO)
at Axceler.Core.Logic.Operations.ActivityByUserOperation.GetActivityByUserDoc(DataTable& dt, String sActivityBy, SPSite site, DataRow& workRow, Boolean isLoggingConnection, List`1 webSelectionList, List`1 listSelectionList, String user)'