What sort of anomalies? I'm curious how you know the chest strap is more accurate so I'm thinking maybe your explanation can help me recognize when my AW sensor based results are off.
It may be that you're having better luck with the HR sensor than I have...some people do have better success than others with optical HR sensors from what I've read. I think you'd know if it was happening to you. I've got a screenshot from Strava of one of the more extreme examples but it shows a couple of things...
You'll notice a couple of things. Firstly that it took nearly 1.5km's to even register anything and then secondly how infrequently it samples, because in theory between 2.0 and 2.4km's there's no fluctuation in my heart rate at all which is really very unlikely.
With a chest strap most of my graphs start out exactly the same; over the first 0.5km's a sharpish rise to maybe 120-130 bpm and then a steadier rise throughout the rest of the run.
It may be that I'm being too pedantic. I'm not in training for the olympics so it doesn't really matter if my heart rate graph is a bit off some days but if I run a personal best or if I'm struggling someday then sometimes the heart rate graph has all of the answers. I find that once I'm warmed up and moving at pace then my heart rate mostly fluctuates in the 150-170 range; that's quite a small window so accuracy is needed or the figures are useless. If the graph says 160 and it was really 170 that's the difference between trying hard and being virtually flat out for me.