There is a known defect loading active Business Process Flow on the Form, when you upgrade from CRM 2016 to Dynamics 365. It does not load for some records which came thru ETL. If you check in Advanced Find including Process Id column, Process Id is NULL for these records.
If you want to show BPF for these records which Process id is NULL, you need to call following JS in the form load event.
function setProcessId() { var processId = Xrm.Page.context.getQueryStringParameters().process; if (processId == null) { //Business Process Flow Id var procesGuid = '03278623-2923-443A-957C-AF56D1B1FC81'; Xrm.Page.data.process.setActiveProcess(procesGuid, function callbackFunction() { }); } }