Hello there @SimoneDeStefano! Let’s try to figure this one out.
Considering the model is reacting to your render distance, this could be related to LODs. You can force the model to a single LOD (LOD 0) for testing. Select the LODSync component in the MetaHuman blueprint, and under details, change NumLODs from 8 to 1 and Forced LOD to 0.
Alternatively, if you have recently updated your project to a new version of Unreal, your current Metahuman could be an older version. If this is the case, a simple re-import/convertion to the latest Metahuman version should fix the problem. Hope this helps!