Workflow won't load due to undefined activity definition. When attempting to load the workflow the following is displayed:
The activity definition may be missing and if this is the case the workflow canvas won't load.
The activity definition may be missing. To confirm this, in the filter navigator type wf_activity.list and filter by the affected workflow version and empty activity definition. For example:
Look up for the activity definition in wf_element_activity, for example:
Take the sys_id of the above record and go back to the wf_activity.list to assign the appropriate activity definition there (use filters to match the sys_id found in the previous step):
Go back to the workflow and it should now load properly.