I conclude that the recursive call (Stitch1DMany calls itself) does not work with processGroups: some output from gdb

Stitch1DMany-[Notice] Stitch1DMany started
GroupWorkspaces-[Notice] GroupWorkspaces successful, Duration 0.00 seconds
420	      AnalysisDataService::Instance().retrieveWS<Workspace>(groupName);
419	  m_outputWorkspace =
420	      AnalysisDataService::Instance().retrieveWS<Workspace>(groupName);
422	  this->setProperty("OutputWorkspace", m_outputWorkspace);
(gdb) p m_outputWorkspace
$22 = {
  px = 0x1894f60,
  pn = {
    pi_ = 0x1894f40
  }
}
(gdb) n
423	  this->setProperty("OutScaleFactors", m_scaleFactors);
424	  return true;  //!!! STOP HERE??
412	  IAlgorithm_sptr groupAlg = createChildAlgorithm("GroupWorkspaces");
368	  std::string outName;
367	  std::string groupName = this->getProperty("OutputWorkspace");
366	  std::vector<std::string> toGroup; // List of workspaces to be grouped
424	  return true;
425	}
Mantid::API::Algorithm::doCallProcessGroups (this=0x7fffffffd150, startTime=...) at Algorithm.cpp:1284
Mantid::API::Algorithm::execute (this=0x7fffffffd150) at Algorithm.cpp:440
Stitch1DManyTest::test_two_groups_scale_factor_from_period_history (this=0x1867380) at Stitch1DManyTest.h:1230
1230	    TS_ASSERT(alg.isExecuted());
1233	    Workspace_sptr outws = alg.getProperty("OutputWorkspace");
1234	    TS_ASSERT(outws);

In Stitch1DManyTest::test_two_groups_scale_factor_from_period_history:
Stitch1DManyTest.h:1234: Error: Assertion failed: outws

Refs #22197