sometimes the instances do not get distributed correctly on base geometry.

this usually happens when base geometry has low face count or uses complicated n-gons. (there may be other cases as well)

a quick fix for this is to subdivide the base geometry a couple of levels before the ia scatter geometry node

this can be done by inserting a subdivision surface modifier in the modifiers panel before the geometry nodes modifier

or alternatively, by using the subdivide mesh geometry node in the geometry nodes editor and then feed the output of it in the ia scatter geometry node base geometry input.

*triangulation may also be needed sometimes

this is a known problem of some geometry nodes:

https://developer.blender.org/T85962

however there are workarounds.

instead of using texture coordinate in the materials:

use an attribute with the name UVMap:

or, for exporting the resulting object with UV maps, after applying the ia scatter modifier, select the object,

go to object data properties tab/panel

go to attributes, select the UVMap attribute, click on the down arrow and select convert attribute

then in the mode select UV Map and click ok.

ia scatter does not come bundled with any models ready for instancing

ia scatter is only the geometry node group addon