Known limitations

We'd rather you read these here than discover them mid-session.

Synchronization scope

Assets, baked data and Terrain data assets are not synchronized (references to assets are).
Prefab Mode (editing prefab assets) is not collaborative.
One component or created hierarchy is limited to 240 KB of serialized data per change.
Whole-component sync uses Unity's serializer: values are applied the way Unity serializes them; 64-bit integer fields above 2^53 may lose precision.

Everyone must open the same committed scene version. Objects that exist only on one machine and were never saved can't be matched.
Session-created objects get different local file ids on each machine when saved — use Share scene with team before committing (see Conflicts & locking).

Remote changes are not added to your Undo stack (by design).
Snapshots contain the scene file only, not referenced assets. Restoring requires reloading the scene.
A restore announced while a realtime server is unavailable is not replayed later — restore again.
Play Mode changes are never shared; remote changes made while you're in Play Mode are applied when you exit.
Domain reloads that take longer than ~15 s lose your locks (you rejoin automatically; your queued edits are re-locked or reverted).

Verified against: the Node/TypeScript server test suites, the C# core test suite and a C#⇄server end-to-end test; Editor-layer code is type-checked against Unity's API in CI. Interactive behavior inside the Unity Editor must be validated in Unity (see unity/SampleProject) before each release.
Unity versions older than 2021.3 are not supported.
One realtime protocol encoding (JSON). Binary encoding is planned behind protocol negotiation.