Should I read this as the Java TreeMap itself is thread unsafe, and the JVM is in a loop, or that the business logic itself was thread unsafe, and just needed to lock around its transactions?
"Note that this implementation is not synchronized. If multiple threads access a map concurrently, and at least one of the threads modifies the map structurally, it must be synchronized externally. (A structural modification is any operation that adds or deletes one or more mappings; merely changing the value associated with an existing key is not a structural modification.) This is typically accomplished by synchronizing on some object that naturally encapsulates the map. If no such object exists, the map should be "wrapped" using the Collections.synchronizedSortedMap method. This is best done at creation time, to prevent accidental unsynchronized access to the map..."
This is so important. The idea that code is thread-safe just because it uses a thread-safe data structure, and its cousin "This is thread-safe, because I have made all these methods synchronized" are... not frequent, but I've seen them expressed more often than I'd like, which is zero times.
The business logic is thread unsafe because it uses a TreeMap concurrently. It should either use something else or lock around all usages of the TreeMap. It does not seem to be "in itself" wrong, meaning for any other cause than the usage of TreeMap.