Hello @Stimpson, John,
welcome to this moderated Azure community forum.
Looking at the documentation, you could reach the limits of your S2:
B2 and S2: Device-to-cloud sends: 120 send operations/sec/unit
I expect these are 4KB chunks and you send at least 480*6=2880 chunks.
Try to scale up with more units if possible.
I also recommend researching the routes towards the cloud ($upstream on the local routes).
You could always open a support ticket so the IoT hub backend is investigated.
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