Deformation and jitter when y position over a few thousands units

Hello I have a character (from mixamo (R.I.P)) on a scene and originally I wanted to set it at some point over clouds generated with enviro, which made me place it at a height of approximately 7000 position.y.

At this position, whenever I play a timeline (while playing or not), the meshes start to get deformations, and child objects such as eyes are jittering and deforming as well.

I tried removing everything but the character, camera, virtual cameras and timeline from the scene but the problem remains.

The problem stops when I put everything at a lower height, let's say more or less with position.y under 1000 (very very approximately).

Do you have any idea why is this happening, and if there is a way to avoid this? Thanks!