Another HR accuracy observation

I run at a consistent pace, and my VO2 max runs around 45.  The graphs that show average heart rate, max heart rate, pace, and so on over time are pretty flat.

Running at my normal pace my HR will get up to 145 -150, and my time in Zone 4 (80% to 90%) is about 30% of the run.

I ran for about a year with a Fenix 5, then about a year with a FR945.  Same consistent results.

Last summer I changed to a Fenix 6, and things continue as normal until about 4 weeks ago, when my HR would be 10 BPM higher than usual, despite running at the same pace and feeling normal.  I was spending twice as much time in Z4, and my VO2 dropped to 40 over several weeks.  My status was unproductive and overreaching, and I was logging way more intensity minutes than before.

Today I went for a run with the F5 to see if the issue is the F6 HR accuracy after firmware 5.0, as I've ready plenty of people report this.

Sure enough, with the F5, my HR was back to normal - mid 140s instead of over 150.  

This is all with the same HR strap.  That's pretty annoying if I logged 4 weeks of crap data.  I'm going to stay with the F5 until I read about something changing with the F5 HR.  Makes it a waste of money for now.