OHR on Fenix 5/5s Plus is more way off than ever

I suspect you may be right. I only had an F5 for a month or 2 before upgrading to F5+. I am finding the F5+ to be somewhat variable even when only walking or sitting at my desk.

I don't recall F5 being quite as inaccurate but as I only had it a short while I could not be sure, but if other people are finding this issue then maybe I wasn't imagining it.

Personally, so far I've found the OHR data from my f5+ corresponds to what I was getting with my f5, and both seem to tally pretty well with readings taken using other methods (e.g. when taking BP, or manually measuring pulse)

My fenix 5+ is doing well in this regard, 24/7 heart rate works nicely and tracks well without any nasty spikes. During exercise though, the watch has to be worn slightly tighter than normal, if not it can lose the signal or track too low.

Also for strength training, I use a chest strap as the movement and deformation of the wrist, coupled with possible light leakage will throw off accuracy slightly causing it to under read and not keep up with changes quickly enough.

Try experimenting with the position, but since the optical reader is essentially the same as the fenix 5 2017, and most reviews mention as good if not better performance, you should get satisfactory results.

I've owned almost every Garmin watch in the Forerunner and Fenix series, and I know that OHR will never be as perfect as a regular strap. But the FR935 really impressed me and showed pretty reliable values overall. When I switched to Fenix 5s Plus and Fenix 5 Plus, I just loved the watches for their great mapping future, and not to mention how light they felt on the arm (at least compared to the old Fenix 3). But, both models are showing some really crazy HR values, and theni mean way off. I'm not even exercising, I can sit still, go for a walk around the corner, and the HR is rocket high.
I've tried all the basic things like restart and yeah, pretty much.
Has anybody else experienced this?

The OHR model is the same on the 935 and the Fenix 5/5 Plus models with the same underlying hardware and software, so from that standpoint there should be very little if any variance between them. Where the difference lies and may be causing the erractic readings is in the respective weights of the watches. The 935 is super light compared to even the 5S (49g vs 65g) and is barely there compared to a 5 Plus (the lightest titanium variant is still 76g). So that means if you're not wearing it tightly the Fenix watches are more prone to "bouncing" on your wrist so that might be causing the differences?

To Carl's point, the weight of the watch puts a bit more work on the hardware to filter out that movement. I've had pretty good luck when running on the road, but running on the trail with big changes in cadence over varied terrain seems to give much worse results. Wear the watch tight and it can be pretty decent. If you feel the watch moving at all, it isn't tight enough. That said I use my HRM-RUN a lot more than just the OHR on the watch.

Thanks for your feedbackl
Yes, I know about the weight difference, and also the size of the watch itself. I know all this things can affect the currency of the heart rate measurement, and that's why I wrote that I have owned quite a few watches the last couple of years. Its not to brag (because I know there is a lot of Garmin-mania people here :) ), I was just to give a hint that I am aware of the most common problems. I thought it was just weird that all of the Plus-devices I have tested seems to have the same problem, even when I am not moving. I actually hoped that there was a bud in the software...

Anyway. I guess I just have to hope for a FR935 Plus or something. A lighter watch with mapping. Thanks again. And happy training ;)