Reset of HR zones every time a new lactate threshold is detected - is it normal?

Weird problem. You solved it?

Disable auto detection of Threshold.

Yes, I've noticed too that Garmin messes up LTHR based zones. Even when a new max HR is detected, it adjusts LTHR based zones, which is completely wrong because those zones are based on lactate threshold and not the max HR. I had to turn auto-detection of Max HR off. 

It's not wrong. In LTHR zones, the max HR is the top end of zone 5 which is above LT. If the LT or MHR changes the zones will change. If you use MHR or HRR zones they will not change unless the MHR or RHR changes.

I am confused. I specifically choose for the zones to be based on LTHR. That means that the zones can change only when LTHR changes because that is how the zones are defined. Tests for LTHR are much more accurate than tests for MHR because MHR is hard to reach for most people. Furthermore Garmin's LTHR test requires an external chest HR monitor. Now, imagine the following situation: I do a run with a wrist sensor which produces a completely bogus HR data, based on which Garmin decides to adjust my MHR to an unrealistic value, based on which it also goes and adjusts all my LTHR based zones. How is that not wrong?

I am aware that zone 5 is above the LT. I don't see any contradiction with that. It goes from LT to whatever the MAX HR is. If the Garmin software can't express Z5 as 100% of LTHR or greater, that is the problem with that software.

What happened the last time when my watch auto-adjusted zones is that it moved my Z5 to start at 104% of LTHR. It also adjusted my Z3 to end at 99% of LTHR. That is definitely wrong! That prompted me to disable the auto-adjustment feature. 

Question is, how you set up your zones, are they reflecting to HRMax or to LTHR.
If to LTHR, Z4 should and on LTHR value, and shouldn't change till LTHR will not change.
It is how it works on my watch.

Hmmm... maybe there is a bug then.

Do the percentages change when you change the LT?

If you reset the zones, do they change back to normal?

When I get some time, I will try to experiment with this, and try to figure out what's going on.

Just disable max hr and put it manually.

Do the percentages change when you change the LT?

I've just tried changing the LT manually and didn't see any effect on the zone percentages.

If you reset the zones, do they change back to normal?

Yes.

Skordilovich said:

Just disable max hr and put it manually.

That's what I had to do. But I still think the existing behavior is a bug that Garmin needs to fix. However I haven't had a chance to test whether this bug still exists in the latest v13.22 firmware.