Do you still need an example of this error? 5.2.0b4…
Hey @topofsteel_1 ,
We have a repro already, thanks!
The root cause of the issue is that during the move to a 64-bit Editor we lost the ability to run the exact same unwrapping code between the Editor platforms. That means that generating lightmapping UVs on Mac will produce a different result than on Windows. For baked lightmaps it manifests itself in triangles sampling from a wrong area in the lightmap, so the failure is not that spectacular.
For realtime lightmaps however, we set per instance UVs (created by Enlighten based on lightmapping UVs). Since unwrapping can produce different results on different platforms it can split the mesh into UV islands differently and that affects the vertex count. This means that currently per instance UVs generated on one platform cannot be applied on another Editor platform.
When not using static batching this results in similar visual errors as you’d get in baked lightmaps. When static batching is enabled, concatenating the vertex buffers makes things go… funky.
We have top men on fixing this issue, but unfortunately it’s quite problematic, so we don’t have the exact timeline. ASAP is all I can say. 
It happens for me sometimes if I update a mesh without changing the geometry. Changing the material or unwrapping a model for example. Otherwise models simply loose their GI build settings and are not visible at run-time. I am not changing platforms. I can fix it be rebuilding the GI. Thank you for your reply.