The Convert Flow Actions utility present under DesignerStudio > System > Upgrade > Upgrade Tools converts only auto generated flow actions prior to PRPC 6.1 to make them compatible with PRPC 6.1 and higher versions.
All non-auto generated flow actions should be manually converted by opening the respective flow actions.
Do the following,
1. Select auto generate HTML option in flow action
2. Click on upgrade button to upgrade the flow action