When I setup the event using DDay.ical I can successfully send the events to a user’s outlook. The problem arises when multiple events are setup at the same time. When this happens all emails are updates to the original task, not new tasks.
I tried adding a name to the event using the .Name property, which results in the event email being an unsupported calendar invite.
Ended up figuring this out through some good old trial and error.
In the end I was not properly setting the UID property to be a completely unique identifier for each event. Changing this to be unique 100% of the time fixed the issue and allowed me to be able to create as many events as I want, any time I want, and have them all appear as separate events instead of updates.