Regarding the manual user synchronization, what would be the effect of taking the action? Will all users that exist in Process Manager/Collaboration Hub will be copied to Workflow Accelerator?
"Synchronize users now, Synchronize users with Workflow Accelerator" will synchronize Process Manager with Workflow Accelerator, so your new users can be included in your approval workflows. Click "Synchronize users now" to create a Workflow Accelerator account for all your Process Manager users who did not have a Workflow Accelerator account before. This should clear up any consistencies.
KBA , BPI-SIG-CA-AWF , Approval Workflow for SAP Signavio , How To
SAP Signavio Process Manager all versions ; Signavio Process Manager all versions