Please check all of the following places, and if you have any obj-saves, obj-deletes, or commits that are referring to your work object or assignment, remove them:
assignment sla activity
work object sla activity
other agent activity
flow action pre and post activities
utility shape activities
The reason to remove the obj-save, obj-delete, and commit operations from those places if they refer to your work object or assignment is that the core level Pega code already does the appropriate operations, and if you introduce extra ones, although most of the time it will work, if there is ever a rollback, issues like the one you are having (flow-removed error) can occur.