This issue is caused by a graphics driver being below our minimum specification.
We therefore recommend that you update your graphics driver, to make sure it meets our standards. Once this is done, you should not encounter this issue anymore.
We have a guide on how you can update your graphic drivers here!
You can find the minimum computer specs for Star Stable Online on our website starstable.com under "Help" -> search for "Technical requirements/specs for Star Stable Online"