为什么我的线程安全字典实现产生数据竞争？

I'm currently implementing a thread-safe dictionary in C# which uses immutable AVL trees as buckets internally. The idea is to provide fast read access without a lock because in my application context, we add entries to this dictionary only at startup and afterwards, values are mostly read (but there still are a few number of writes).I'm currently implementing a thread-safe dictio