Hart rate not synced

Same answer as in the other thread you posted to:

It could be a problem of a full or dammaged storage on the device, or perhaps a problem of syncing.

As for the storage - connect to the watch with the USB cable, and check out the free space on it (on Windows in File Explorer, using the Properties of the drive). You can also test the storage - again with the built-in function in File Explorer, or with some dedicated USB storage repair tool.

As for the syncing, review the Sync Audits on the GC app (Menu » Settings » Device Sync Audit), and search for any errors or suspicious messages in them. Note that you can use the buttons at the bottom to navigate among the past audits.

Jikes. There are 358 items in that "device sync" part... Around the date the sync stopped I seen nothing that catches my eye. 

Checking for errors yields "no errors found" 

10.8Mb out of 11.8 are available. As for memory : according to the app I have 160K and 8 slots available. I doubt if that's a problem? 10.8Mb out of 11.8 are available. 

Yes, looks all right. Try signing out of the app (Menu » Settings » Sign out), and signing back in, and then keep an eye on the HR graph. When you see any drop out of the data again, review the Sync Audit for the time around the beginning of the drop out, and search for errors. Especially in the section Upload, when it contains the word MONITORING. You can also check the folder //GARMIN/Monitoring/ on the device and looking at the files it contains - checking their size and dates. And you can also try syncing over the USB cable to Garmin Express.

Thank you for your efforts to help me out,

I have tried everything. Including a complete reset of the watch (factory restore), an uninstall and re-install of the app, I can't for the life of me figure out how to remove ALL data, and yet without watchfaces, without widgets, without anything installed on the watch : I have a hartbeat on the watch, but the app refuses to acknowledge. I will have to wait and see if it registers sleep tonight, but I am almost certain it will not. I am seriously to old for his (...).

Why is this entire Garmin thing turning into one gigantic frustration??? Even this website is to hard for me. My letters are suddenly huge. Sorry. I. Don't. Understand. 

Try calling directy the Support (find the local number on the website support.garmin.com), it may be easier if they lead you through the necessary steps by phone.

In the Netherlands? Please allow me to laugh out loud. Very long and very hard. 

I will explain after i stop laughing. 

1: (any) Company and telephone? Nope. Nope nope. IF they have a phone  number it will be at 1 euro per minute. And they will hang up during the waiting cue after 59 minutes. 

2:IF they have a phone number it is where you can buy their equipment. It's not meant for service.

3: IF you manage to speak to a human, they will tell you to go to the internets. Not call them anymore. Ever. 

4:I have send 4(!) emails already since jun-1 when I started using this watch. I got 0 responses. Because: Netherlands. Customers may buy, and must shut up. Customers are there to bring in money and nothing else. 

This is not Garmin specific behavior. Don't worry. It's any and all (large) companies over here.  Customer service costs money. Money that goes out of the profit. That's why this side of the world is dependent on forums and other users. That's why I am so reluctant to buy any new equipment. I am to old to understand and learn all this new stuff (54...)

I have a hartbeat on the watch, but the app refuses to acknowledge.

What does it exactly mean? When you are on the main screen, do you see the HR changing live? Is the watch connected to the phone (green dot on the circle around the device symbol)?