This has been going on for weeks. Super slow download speeds but my upload speeds are much better. This can't be network congestion because it will still happen at 4am. I am on the 10GB plan and never go over it. Apple shouldn't even allow Xfintiy to sell iPhone with this kind of speed.
Your download speed is very close to the intentionally throttled 600k per second throughput rate used when folks exceed data-caps via hot-spot usage. Your terms of service may provide any relevant details if that is the case. If such intentional throttling is an issue, you should find that there are alternative plans/tiers where you can pay more to increase the throttle rate and/or raise any cap at which throttling will occur.