UE5: After used the “Merge actor” tool, the merged mesh is not visible on the reflection surface when it is outside of the screen, but unmerged actors are still visible on the reflection surface even when they are outside of the screen. Is this is a mistake?
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I think that’s because it’s screen space reflections ( or do you have lumen reflections configured? ).
With SSR, the object has to be on the screen to reflect.
The problem is that some objects, such as the two cubes in the picture, are visible on the reflection surface when they are off-screen. Why?
Ok, then it’s not SSR. Meh… reflections is a whole ‘thing’.
I suggest you export the merged meshes and reimport them as fbx. Maybe youll get the results toure looking for.
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I think you have to do “generate mesh distance field” again, within the properties of the static mesh 
I just tried to turn off and turn on the distance field again, and restart the project, the problem still exists
*Keep waiting for answers. Thank you
I need answers too 
Thank you! This actually worked for me.
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The issue is way deeper than this
- according to my experience merged actors are excluded from lumen calculations. This leads to missing in reflections, but causes shadow and lighting issues as well.
You can check this by switching to lumen scene overview - merged objects are missing
There is a simple solution for this, that I found reading this article - in merging options you have to enable “Allow Distance Field” - this will allow object to appear in lumen calculations - this will leads to visibility in reflections and fixing shadow and lighting issues.
There is even one workaround if above solution will not work - and it was suggested as well few lines above - exporting and re-importing mesh. This will by default generate distance fields.
CONCLUSION: Distance fields on meshes are essential for lumen to function correctly. Without them mesh is not inherit to Lumen calculations causing reflection, shadow and light issues.