If the mouths on screen move before the words arrive (or after), the drift is almost always introduced by buffering or processing delay somewhere in the signal path — not by your sound board.
Where the delay usually comes from
- Audio delay compensation in OBS. Right-click the audio source in the Audio Mixer → Properties → Sync Offset. If the room's PA and the stream feed use different audio paths, one can arrive milliseconds ahead of the other. Nudge the offset in 20-40ms steps while watching a person speak on camera until it lines up.
- Wireless audio transmission. Any wireless link (wireless in-ear packs feeding a recorder, a Bluetooth-based audio interface) adds latency that wired connections don't. If sync drifts more as a service goes on, suspect a wireless hop in the chain.
- Platform-side buffering. YouTube/Facebook add their own processing delay before viewers see it — this is normal and not fixable on your end, but it should be consistent, not drifting further out of sync as the stream continues.
If it drifts progressively worse (not just offset, but widening)
That's a different problem — a clock sync issue between your video source and audio source, common with certain HDMI capture devices. Restarting the capture device/software usually resets it. If it recurs every service, note which capture card and check for a firmware update.
Quick check
Test with a simple clap in front of a camera before service. If the clap sound matches the visual clap in your OBS preview, your local sync is fine and any drift viewers report is downstream (their device, their connection) — not yours.