dataflow gen2 failed after change owner

I have created a dataflow gen2 using my own account, now I want to change the owner of the dataflow to a service account. This has worked in the past, but failed for this flow. Below is what I have done:

1. add the service account as workspace admin so that it has access to all Fabric workspace items.

2. select the dataflow- right click- selelct "setting" - change the owner using "take over" option - go to the data flow again, under 'manage connections' - current project, choose to unlink the connection to Fabric warehouse - go to 'global permissions' -delete the 'warehouse' connection - then create a new connection using the service account, gateway option= 'none' (because source data use Power BI dataflow legacy) - I then try to add the warehouse in the destination page - but it generates connection failure. 

3. I have also tried updating the warehouse connection in Power BI view - data source credtionals section. It doesn't solve the issue.

It's confusing because I have managed to change data flow owner before in the same way. Those data flows are in the same workspace, using the same data source.

Raza