Recreate:
Add a Change Assembly Version task to an existing job (probably doesn't matter if it already exists or not)
Set a value in the Assembly Version field
Save
Edit the job again (Configure)
The value that was set in the Assembly Version field is now blank, so when the job is saved, it will no longer have that field populated, and the task will fail.
I reverted to the previous release of the plugin, and this does not happen.