Packaging with with a nativized blueprint that contains a TMap with a TSubclassOf pointer as a Key causes errors, causing the packaging attempt to fail.
Regression?: No
Compiling the code for the TMap using a TSubclassOf pointer as a Key failed in 4.18, blocking this from being tested.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-61275 in the post.