Sync periodically needs to refresh the access token used to control the sync session. When this happens, it crashes the app with:

2020-06-09 08:02:33.254 10985-11022/com.mongodb.tasktracker E/REALM: /Users/cm/Realm/realm-java-release/realm/realm-library/src/main/cpp/jni_util/java_class.cpp:50: [realm-core-10.0.0-beta.1] Assertion failed: cls with (class_name) = ["io/realm/internal/objectstore/OsJavaNetworkTransport$Response"]
<backtrace not supported on this platform>!!! IMPORTANT: Please send this log and info about Realm SDK version and other relevant reproduction info to help@realm.io.
2020-06-09 08:02:33.254 10985-11022/com.mongodb.tasktracker A/libc: Fatal signal 6 (SIGABRT), code -1 (SI_QUEUE) in tid 11022 (Thread-3), pid 10985 (odb.tasktracker)

The hypothesis is that the callback to do this happen on the Sync Client C++ thread, which is started from C++ and thus does not have access to the Java class loader. So it crashes when trying to find the response class.