Recording and playing back TimeSynchronizer reliably

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Given two topics synchronized with either Exact or ApproximateTimeSynchronizer, when running the system versus playing back the recorded bag file, due to various factors we cannot guarantee that the same set of messages will be paired up, so reproducibility is lost. Even running rosbag play --rate 0.2 I occasionally observe that the synchronisation gives differing results between runs.

How have other people addressed this? I imagine something like an enhanced sync node could record the timestamps of the messages it synced when running in real time, then when using use_sim_time it uses the recorded timestamps to do the syncing. Does such a node exist?