Livesync was running for a while (months) without any major issues. Few days back it was suspended and workerThreads=4 option was added.
Task stalled no errors in log at all. Last livesync cycle that was processed finished without any apparent issues (last sync event from connector was processed - checked via audit), then task just did nothing for 18 hours, while still being "in progress".
Livesync task in GUI also doesn't show any worker activity even when task processes events (see attached img).
There's also a possibility that this will have to be backported to 4.0.3 (will see bit later).