The type 'Flow' does not seem to connect to both elements in ArchiMate (connecting at one end only).
If your model is following ArchiMate rules, the system allow you to connect properly. Please check the ArchiMate modelling guideline to see if you are modeling follows the notation rules.
More information in User Guide
KBA , BPI-SIG-PM-MOD-EDT , Graphical Editor for SAP Signavio Process Manager , How To