We shutdown both Appian engine and jboss due to our oracle database patch.

...light processes now. We havnt deployed any new processes during the shutdown. Have you seen this behavior? and any idea what would cause this?

Has the deployment service account been deactivated?

No. All the other service accounts are still active.

If this is expected based on your knowledge about the security of the process model then this is definitely something that has to be fixed since it indicates an issue with the design of the model.

What you want to review is if there are other process instances that completed fine in the past, if you have those then you review who started the process and check if they lacked privileges, most likely they didn't and that's why until now when the users without privileges try to start that sub-process they get that error.

The fact that you see this after the restart looks more like a coincidence, there's nothing in a restart that can change something that is expected to happen according to the design of the model; assuming that what you got was a set of emails they could be queued emails whose alerts you had already received and went unnoticed because of the queued emails.

If after the restart you got both the alerts and the emails then that means that it was until that time when these sub-processes were attempted to be started.

In general there's more investigation that you will need to perform, including any changes in group membership for users; if someone removed a rule from a group or removed users from a group privileges can be now more restrictive making this to happen; I suggest you do not center the investigation in the restart.