realm/realm-swift v10.42.2 on GitHub

Add support for logging messages sent by the server. (Core #6476)
Unknown protocol errors received from the baas server will no longer cause the application to crash if a valid error action is also received. Unknown error actions will be treated as an ApplicationBug error action and will cause sync to fail with an error via the sync error handler. (Core #6885)
Some sync error messages now contain more information about what went wrong.

The MultipleSyncAgents exception from opening a synchronized Realm in multiple processes at once no longer leaves the sync client in an invalid state. (Core #6868, since v10.36.0)
Testing the size of a collection of links against zero would sometimes fail (sometimes = "difficult to explain"). In particular: (Core #6850, since v10.41.0)
When async writes triggered a file compaction some internal state could be corrupted, leading to later crashes in the slab allocator. This typically resulted in the "ref + size <= next->first" assertion failure, but other failures were possible. Many issues reported; see Core #6340. (since 10.35.0)
Realm.Configuration.maximumNumberOfActiveVersions now handles intermediate versions which have been cleaned up correctly and checks the number of live versions rather than the number of versions between the oldest live version and current version (since 10.35.0).
If the client disconnected between uploading a change to flexible sync subscriptions and receiving the new object data from the server resulting from that subscription change, the next connection to the server would sometimes result in a client reset (Core #6966, since v10.21.1).

RLMApp has localAppName and localAppVersion fields which never ended up being used for anything and are now deprecated.
RLMSyncAuthError has not been used since v10.0.0 and is now deprecated.