I wonder if it has anything to do with it being defined in intrinisics part of Kotlin code. Mouseover shows it is using kotlin_metadata:

JVM source does exist though: https://github.com/JetBrains/kotlin/blob/master/libraries/stdlib/jvm/src/kotlin/coroutines/intrinsics/IntrinsicsJvm.kt#L99

tested with several Kotlin versions, Gradle versions and IntelliJ versions; the issue remains. I suspect the common implementation contains the .kotlin_metadata that provides the needed info to retrieve the JVM implementation, but IntelliJ does not manage to retrieve it. I can find the implementation in the "External Libraries" section of the Project, so it is there. As I'm currently running on a rather specific setup, I'll first try to reproduce on another machine and log an issue for it if I can reproduce.