Heart rate monitor only working occasionally

[theopacus]

Got a Blaze for Christmas and the first few days it worked without any hassle. When i got it i did the following:

1. Charged it to full

2. Paired it with my phone and upgraded the firmware as per. instructions on screen.

After four days, the heart rate monitor stopped working. Crawled Google and these forums and found a solution that fixed it: Shutting it down from the settings menu, and turning it back on again. 

Yesterday, it stopped working again. Now, however, it only works for 1-2 minutes after shutting the Blaze off and turning it back on. It´s the same wether i shut it of and turn it back on from the menu, or if i "hard restart" it by holding left and lower right buttons for 10-12 seconds.

In addition, it´s has severe problems syncing with my phone from time to time. iPhone 7 Plus, iOS 11.2.1

More info and things I´ve tried:

Both lights are flashing, as they should.

Device is not sweaty, as I haven´t worked out using it yet. 
I´ve tried it on both arms, both loose and very tight.

I´ve cleaned the sensor.

I´ve reinstalled the app on my iPhone, deleted the blaze from my settings and paired it anew. 

Monitoring Heart Rate has been tried both on "Auto" and "On". 

I´ve removed all other devices paired with my phone so only the Blaze remains. I´ve also, as previously mentioned, removed the blaze, and paired it again.

Should i get a replacement, or should i wait for a software update? I really suspect this is a software issue and not a firmware issue, seeing that so many others are experienceing similar problems. 

[AlejandraFitbit]

It's great to see you around @theopacus and thanks for troubleshooting this by yourself.

In this post and here, you will be able to see some things that might be affecting your heart rate reading and some tips to improve it. Regarding the syncing, I recommend taking a look at the Having trouble syncing? post and follow the instructions provided there.

I hope this helps, let me know the outcome.