ChunkManager's API exposes several methods that are not safe to be called when that ChunkManager was constructed https://github.com/mongodb/mongo/blob/4b43a2f98e9bb481d71f57f9773f7c0415c1fdb9/src/mongo/s/chunk_manager.h#L625. Examples of unsafe methods are getNextChunkOnShard(), getAllShardIds() and getNShardsOwningChunks(). SERVER-87197 added tripwire assertions to catch unsafe usages, but a more permanent improvement is to change the ChunkManager API so that such unsafe access are not even possible programatically.