Inspire 3 heart rate tracking becoming less accurate

[nms1]

Does anyone else have issues with their Inspire 3 becoming less accurate when tracking HR?I wonder if it's just getting old. I have more and more examples of my HR showing as below my active zone in the middle of an intense workout. Today I could barely catch my breath and it showed as 89.

[lmacmil]

I have found that in very warm weather (it was already 80F when I walked this morning), the sweat causes the Inspire to move around and/or lose contact which results in a very erratic heartrate graph.  See the attached plot from yesterday.  I walk at a pretty steady pace and never stopped.  I don't see graphs like this in cooler weather when I'm not sweating.  When it's making consistent contact my HR is pretty steady in the 120 to 130 range. 

[nms1]

I do take it off and wipe it in the gym just in case. I live in a country where the temperature never falls below 25c/75c so sweat is a year-round issue!

[lmacmil]

Today I wore the Fitbit one notch tighter than usual.  I didn't see the wild variations in heartrate but my heartrate also showed a much lower reading than previous walks over the same route at the same pace.  Not sure what to make of this.