If Stingray is the problem: During the early project phase Stingray was discontinued. They knew that for a really long time (at least 6 years) and still continued with it.

I however doubt that Stingray is the problem because

• these problems persist since launch
• most games on other older engines run smoothly if properly optimized
• how is it possible that they picked this engine in 2018, when GPUs from that timeframe have serious performance problems? The only explanations are: Either they never tested this at the start or they added a bunch of problematic stuff during development in their code

So anyway it's entirely their fault.