System Information
Fedora 29, 970m

Blender Version
Broken: rB0c8aa85069fa
Worked: NA

Short description of error
Lights appear to not cast shadows if they are part of an collection instance.
Lights in the collection itself work though.

Exact steps for others to reproduce the error

• open attached .blend
• switch to rendered view (same is true for lookdev with Scene Lights option ON)
• there is a collection with one light (casting shadows)
• there is an instance of that collection (light in that instance appears to not cast a shadow)

while instancing of collections of lights might not be a very common practice, it is mostly relevant when linking such a collection from another blend.
( and the Instance Collectionsoption is enabled by default when linking a collection -- if that option is disabled during linking, shadows work... )