Jacky is correct, that is the engines occlusion culling working to help optimize performance.
There are a couple of ways to go about looking into this.
You can visually test your occlusion culling by using the console command r.VisualizeOccludedPrimities 1. This will only be visible in the editor and not while in PIE/Simulate. This will place a green bounding box around the meshes that are occluded. This bounds can be controlled by the Bounds Scale for each mesh in the Details panel when selected. This may not be the best way to fix this issue and I would recommend enabling HZBOcclusion. You can do this by using the console command r.HZBOcclusion 1.
HZB Occlusion will use an approximation for bounds depending on the size of the mesh rather than strictly using the bounds that are set. If you’re using the console command to visualize the occluded primitives you can see that the mesh will become unoccluded before being visible. There are still improvements to be made with this, which is why it is disabled by default right now, but it can help in situations like this without the need to increase the bounds scale on multiple meshes.
If you do go the bounds scale route only increase where needed and increment in the decimal range. The default is 1.0. So try 1.15 and see if that works. If not just increase by .05 or .1 until you get the result you need. If you need to see the bounds of each mesh you can enable this in the Show > Advanced > Bounds. Then when you select the mesh you will see a representation of the bounds that you adjust in the details panel.
I hope this helps.
Tim