@Skaughtto if you have working to hard what easy one day can feel very hard the next day, have a look at my post, even though the sample is power data from cycling its quite relational to HR as HR relative lag and show its effect to late

I commute so I've ridden the same route 100's of times. As soon as I input my custom heart rate zones, which are not far off from the default, my relative effort scores changed dramatically. I was using relative effort as a metric to gauge my training load week by week, but it feels like it is no longer accurate.

If someone could test the default settings and then making a slight adjustment to the zones to replicate the effect, I'd be interested to know if it's a bug in the RE calculation.

Also, if I use the Perceived Exertion slider (for rides when I don't have my heart rate monitor) relative effort values are very inconsistent. At times what's calculated when wearing the HRM is 3x to 4x lower.

Again, if someone could test this same scenario (use custom hear rate zones and check relative effort scores) I would appreciate it.

Have you tried the chrome browser extension https://thomaschampagne.github.io/elevate/#/landing you might be able to check & compare between the two, as your asking people to modify their settings, which most won't. when riding over 500km a week I rely on power, HR is very deceptive to how much your doing, I could riding at aerobic threshold around 130 BPM and yet my perceived effort is at 80%, and when I race I am at 155 BPM for hours.  

I have custom HR zones (Z2>=110, Z3>=126, Z4>=143,Z5>=160) for the last two years, and I can confirm your findings. My Strava calculated relative efforts using HR data are very low compared to those calculated by using perceived effort (the slider).

Not only that, but the estimated calories output is waaay off (also very low). I don't have powermeter, but the avg power seems to be correct compared to the other calculators found online (I have tested it on long and constant uphills). As a result, when I convert calories to kilojoules, my body seems to have insanely and impossibly high efficiency ranging from 60% to 75% instead of being very close to 25% which is the normal energy efficiency for humans. My bodyweight and bike weight are correctly entered into Strava settings.

I'm expecting a Stages power meter to arrive in the mail soon. I'll let you know how it affects relative effort values.

I've found the opposite.  RE was very inaccurate until I switched to custom zones.  Rides with friends with very similar fitness and ability would put me in the 100s and them in the 400s. Still.not great, and I don't pay much attention to it.  Overall, RE and any HR based measures are very inferior to Power with accurate zones for training and effort.  HR and HRV are great as secondary measures that show what your condition is vs your baseline.

Relative Effort is based solely on HR, so power should not affect it.  However, once you have an accurate FTP, you should be able to adjust your custom HR zones to match, and then see how that affects RE.  (Fitness and Freshness does change with Power, BTW).

yes, now in cycling power has been the biggest change and the ability, we have seen this in pro-cycling as now young athletes are producing the results as they are taught to train correctly & not overtrain which was taking years to learn that feel,  HRV is a tool to check how your body is recovering whilst resting(which is just as important as training), which may mean you dont another session as it will be unproductive. @Dekays  you might want to look into HRV & meditation and how they being used together, this is a good blog https://www.diygenius.com/meditation-and-heart-rate-variability-training/ 

I've completed FTP tests via Zwift, so I had some power data from indoor training. My outdoor activities seem about the same. Yesterday I rode without a HR sensor and Strava didn't provide a Relative Effort value, so yeah - solely HR based. 

I think I adjusted the custom zones by a very small amount from the default values and saw radical changes in RE, so it was a bit startling. Maybe I'll ignore it for now. Lately I've been looking into polarized training (80/20) and I'll be spending more time chilling in heart rate Zone 2.