You need to update to 5.12 and reduce your clip_size:

quote:

clip_size
This value (default 0.5) gives the minimum number of pixels that must
be covered by a model triangle for being rendered. With the default
value, model triangles are not rendered if they are smaller than half
a pixel. This increases the frame rate, but can lead to "holes" in
ill constructed high polygon models. When using high polygon models
clip_size should be set to 0.


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