Drew Kerman posted an intermittent bug showing NullReferenceExceptions in the log during asteroid spawns in timewarp. Another player, N3N, reported the same problem but said that reinstalling some (unspecified) third-party mods fixed it.

I cannot reproduce this bug on a clean game of KSP; given this and N3N's report, it is likely a mod conflict of some sort.

Closing as there have been no other reports of this issue in 2 years.