CRM 2020 R1 ArgObj property not working?

List=CRM.GetBlock("maProjectUserGrid");
List.prevURL=sURL;

FilterBox=CRM.GetBlock("maProjectUserFilterBox");
FilterBox.NewLine = false;
FilterBox.DisplayForm = false;
FilterBox.DisplayButton(Button_Default) = false;
FilterBox.ButtonLocation=Bottom;
FilterBox.ShowValidationErrors = false;
FilterBox.RefreshFromContent = true;

container = CRM.GetBlock('container');
container.AddBlock(List);
List.ArgObj = FilterBox;

I've used code similar to this for years.  With CRM 2020 R1 the filter does nothing.  In the SQL logs from CRM 2018 and CRM 2020 R1 after clicking the 'Filter' button:

CRM 2018:

Apr 7 2020 13:43:43.332 5648 5056 3 fselectsql,time,sql 79 select count(*) as fcount from vmaProject  WITH (NOLOCK)  WHERE (prjct_UserId=1 OR prjct_LeadConsultant=1 OR prjct_Consultant2=1 OR prjct_Consultant3=1) AND  prjct_stage = N'Planning'
Apr 7 2020 13:43:43.348 5648 5056 3 fselectsql,time,sql 15 SELECT prjct_referenceid, prjct_salesorderno, prjct_name, prjct_stage, prjct_status, prjct_golivedate, prjct_companyid, prjct_maprojectid FROM ( select prjct_referenceid, prjct_salesorderno, prjct_name, prjct_stage, prjct_status, prjct_golivedate, prjct_companyid, prjct_maprojectid , ROW_NUMBER() over(ORDER BY  prjct_referenceid DESC , prjct_maProjectID DESC ) AS rowranking  from vmaProject  WITH (NOLOCK)  WHERE (prjct_UserId=1 OR prjct_LeadConsultant=1 OR prjct_Consultant2=1 OR prjct_Consultant3=1) AND  prjct_stage = N'Planning'  ) as A  WHERE rowranking > 0 and rowranking < 11


CRM 2020:

Apr 7 2020 14:26:31.704 3392 4284 3 fselectsql,time,sql 0 select count(*) as fcount from vmaProject  WITH (NOLOCK)  WHERE (prjct_UserId=1 OR prjct_LeadConsultant=1 OR prjct_Consultant2=1 OR prjct_Consultant3=1)
Apr 7 2020 14:26:31.710 3392 4284 3 fselectsql,time,sql 0 SELECT prjct_referenceid, prjct_salesorderno, prjct_name, prjct_stage, prjct_status, prjct_golivedate, prjct_companyid, prjct_maprojectid FROM ( select prjct_referenceid, prjct_salesorderno, prjct_name, prjct_stage, prjct_status, prjct_golivedate, prjct_companyid, prjct_maprojectid , ROW_NUMBER() over(ORDER BY  prjct_referenceid DESC , prjct_maProjectID DESC ) AS rowranking  from vmaProject  WITH (NOLOCK)  WHERE (prjct_UserId=1 OR prjct_LeadConsultant=1 OR prjct_Consultant2=1 OR prjct_Consultant3=1)  ) as A  WHERE rowranking > 0 and rowranking < 11

Clearly in CRM 2018 the WHERE clause is expanded to include the Filterbox field 'prjct_stage', but not in CRM 2020 R1.

Has anyone else seen this?

Is there a workaround?

Thanks, Paul