hey there,
on first glance I would assume, that thunderbolt does not have enough bandwidth to fully use the eGPU. Additionally I do not know how response times are with external GPUs. I could imagine, that depending on the system setup it could cause timeouts.
At first glance I doubt that a bug is causing this. Some Games (and other software) might be more susceptible to timeout errors than others, but all in all it sounds like a hardware issue to me rather than a bug in the game.
Is there any way you could share your system logs? maybe the team can find issues there?