Is this really an AWS issue? Sounds like you were just burning CPU cycles, which is not AWS related. WebSockets makes it sound like it was a data transfer or API gateway cost.
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I doubt they would have even noticed this outrageous cost if they were running on bare-metal Xeons or Ryzen colo'd servers. You can rent real 44-core Xeon servers for like, $250/month.
So yes, it's an AWS issue.
You can rent real 44-core Xeon servers for like, $250/month.
Where, for instance ?AWS: E5-2680 v4 (2016)
Hetzner: Ryzen 5 (2019)