In case you are referring to the Groom, I noticed the same problems.
In 5.3, the Groom disappearing at distance could be solved by adjusting the LOD_Sync settings and setting it to 0.
In 5.4, its a bit more work:
Open the Metahuman Blueprint, click here in the outliner:
And then set forced lod to 0
Then you click on the Groom, e.g. Hair. and Search for LOD on the Details Panel.
I then set it to Never Distance Cull
And lastly, you open up your Groom, go to the LOD tab and set LOD mode to Manual
That should fix it 