I have this issue. I have a 20-30 beat discrepancy in my power zone and HR zone. If I’m doing endurance or vo2 max, i’m in the “right” power zone but my HR one doesn’t match. At the beginning of vo2 max I’m 50 beats below and at the end I’m 20 beats below. Endurance I’m 20-25 beats below endurance HR when my power is in endurance zone. Does lactic acid build up always coincide with HR in terms of zones? A lot of the times my legs my be burning/hurting in a threshold or vo2 max workout but my HR is still in endurance or low tempo zone.
Some coaches say yes, to trigger the correct adaptions. Ride 1/2 to HR and anything above to power (ignoring HR, unless you have a medical problem of course). Although with TR workouts myself I tend to use power all the time as their workouts tend to cross multiple zones. Only outside do I use HR alone, if I’m doing a pure Z1 recovery ride or I want to stay fresh for the next day (I tend to keep it below 75%MHR (approximately Z2 depending who’s zone you are looking at 
)).
As to your break I doubt it would have done any harm. I use carb drink and avoid gels unless its a race or an emergency pick me up but we are all different.
Number one rule for me, don’t over think it and just ride
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the coaches I follow, the ones that have been using the aerobic decoupling metric for a long time, my understanding is that answer is no. It was first used as a metric to determine when you’ve done enough low aerobic training, and it was time to move on to doing tempo and threshold work. It has also been used on higher intensity (upper tempo and threshold) intervals as a signal to do more endurance (low aerobic) work.
However, it is hard to give advice without knowing more about your training and the details of that ride (hydration, nutrition). For example did you jump from doing 1-2 hour endurance rides to this long/steady endurance? Just one of a handful of questions off the top of my head.
Also, your entire ride’s Pw:Hr in TrainingPeaks is less interesting than removing the first 30 minutes and looking at decoupling of the steady portion (including break) after the warmup.
The Garmin auto-lap is a distraction and not really helpful, from it I can tell you the hour to hour decoupling but nothing else. TrainingPeaks premium has tools to select a portion of the ride and get Pw:Hr. And other analytic platforms have it as well.
The one thing I can say for sure - don’t worry about that 6-8 minute break and “reducing effectiveness” of the workout.
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Thank you for the insights and information.
I appreciate that, and I guess I was looking for more general guidelines as to whether I am doing Zone 2 “the right way.” FWIW, I consumed about 90g of carbs and a 26 ounces of hydration mix (electrolytes) per hour.
Last year I tried to build up to 6-hour long steady endurance rides, adding a half hour each week, but this was the first time I was able to do one on a course that allowed me to ride without stopping or breaking my pace for the duration of the ride. Also, I probably was not always very disciplined about staying exclusively in Zone 2. 
Thanks for the tip. I keep in in mind going forward. FYI–Excluding the first 30 minutes and the cooldown, Pw:Hr for that ride is 7.44%.
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the “right way” is in the eye of the beholder LOL. For me its doing more 2-4 hour steady endurance training rides at 66-79% ftp and saving the long rides for group adventures. But if you are training for ultra events, that one looks pretty good and after some more steady endurance riding your decoupling will likely come down. Anything under 5% is a win, given that outside you can’t control every environmental variable.
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I’m in this spot where it seems almost impossible to be in a true zone 2 (as I understood it from running). With running, it was pretty simple being purely HR-based. Just set my zones, and run within that zone. With cycling, on the Trainer, I have to work really hard to get my HR up, so on endurance rides on TR, I’m mostly not even in zone 2 HR. Sweet spot rides put my HR squarely in zone 2. But then that’s not zone 2 power and it’s definitely not chill.
Riding outside, I rarely have stretches of flat road. Hilly and lots of false flats. Even the latter easily gets my HR up and I’m not trying to go full gas or anything, just trying to maintain a certain cadence. But yea I easily shoot past zone 2 riding outside. I think a power meter on outdoor rides would be really useful b/c it seems like this would be far more accurate in determining if you’re in zone 2 vs reading HR. Or is it?
Cycling is power referenced to HR, so yes, having a power meter outside is really really useful. For example you said climbing to maintain cadence, well, if the grade is slowly increasing, your power is increasing to maintain cadence. Sometimes I get overly excited before hard intervals, and can see HR slowly increase due to excitement. Sometimes a car comes close and my HR shoots up. Generally my HR is stable relative to steady power, but there are exceptions both indoors and outdoors. Hard to say anything with the info given. Hope that helps.
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With me it’s drinking and especially eating. Guaranteed to take me from 120bpm up towards 130bpm on a steady Z2 ride.
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Crazy! Never see that. Just points out how HR can be very individual. Starting with power & HR zones.
Is it the eating and drinking though or sitting up to eat and drink? The same happens to me but it is because the sitting more upright to eat and drink. Even if I sit more upright and dont drink or eat I get the same HR response, just a thought and wondered if it really the eating and drinking. Inside I used to think is was moving out of the fan stream but it isnt for me.
It’s also that it disrupts your breathing rhytm which then raises heart rate.
All of the above, but mostly I’m greedy so the idea of food makes me giddy. 