I'll try to explain everything the best I can.
While I'm running, everything works fine. I get all the data without any issues. When I'm done with the workout (run) and it's time to sync, problems happen. The strap itself doesn't automatically download the data and merge it with the data from the watch. If I just let the watch sync the activity with Garmin Connect, the trainning effect reported on the watch is not the one calculated with the strap data. How do I know? Because when I go to the activity (on the watch, once it has synced the activity with Garmin Connect) and make it download the HR data stored, it changes (the new report I get is more in tune with what I would expect from the workout). So, up to this point, the HR data doesn't automatically sync. After downloading the HR data (again, once the activity has been synced with Garmin Connect) and updating the activity on the watch, I get a new activity on the Garmin Connect feed instead of updating the previous one.
Now, I'll talk about what happens if I download the HR data just when I finish the workout. Once I'm on the summary screen after the workout, making the watch download the HR data makes it so that the watch doesn't sync the activity with Garmin Connect. I have to connect the watch to the computer and use Garmin Express to make it sync it and have it displayed on the feed. (Without doing this, not only do I not get the activity itself, but any data whatsoever in regards to steps or any other metric on the kind)
For context, I use it with a Forerunner 745.
Thank you for taking the time to read this. :D