My guess would be that you have become highly trained in Z2-3 and have a very small Z1. Meaning you may have Aerobic Deficiency Syndrome (ADS).
As you train more in expanding your Z1, your Z2-3 efficiency will decrease as you’re not spending time training those zones. However, once you build up your Z1 HR to be within 10% of your Z2 HR, your Z1 will be big enough/efficient/fast enough for you to move “lightly” while staying in an Aerobic zone.
If you haven’t yet, perform the AeT test to see where your zones are – https://uphillathlete.com/aerobic-anaerobic-threshold-self-assessment/
Hope that helps!