Alta HR topped registering my treadmill power walks

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Alta HR is about a year and half old.  It has always been very accurate registering my exercise until the last couple of months.  

The majority of my exercise consists of treadmill power walks.  It has always registered them consistently regarding time, HR, steps, etc.

Now, it will either only register half or none of the exercise.  

I reset the fitbit itself last week, and it registered the exercise accurately for a day or two, but has gone back to being inaccurate.

I really love to see the data it produces when it is working properly, so if it is shot, I need to get another device.  

If so, I'd love to hear recommendations, including non-fitbit options.

Thanks,

AD

Moderator edit: subject for clarity 

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On 1/25, it tracked my morning exercise perfectly but completely missed the same exercise (30 minute, 2 mile treadmill walk) that same afternoon.

I ordered an Inspire HR and will report back as to how it performs.

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My post title was edited for clarity, which I do appreciate, but I am hoping the moderator will edit again for the spelling issue.

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Unfortunately, I am experiencing the same issue with the new Inspire HR.  Yesterday, it perfectly tracked my morning exercise and missed the afternoon one which was the same.

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I'm done with them.  Devices worked perfectly fine for over a year, and now I can't get my old or new one to register some or all of my exercise.  I'm returning this **ahem** Inpire.