Activity Issue, Long Updates on iWatch

I just updated my iPhone to 27.0.1 from 26.6.2. It took 45 minutes.

Then I noticed that my watch (Series 11) was in the midst of "downloading" its update to go from 26.6 to 27.0.1; unknown to me, it had been set for "automatic updates" (probably from an earlier update and I wasn't aware of the change). So I placed the watch on its charger with the iPhone nearby, and observed it to proceed.

The download took about 45 minutes; our internet and WiFi provides about 550 Mbps, so I suspect some of this slowness was related to WheelieNick's explanation about use of BlueTooth, which of course is quite slow. But the download was big, over 2 GB, and a lot of time was spent in "preparing" after the download finished. The actual "installing" step was just a few minutes at the end of the process. The total time for the watch to go from 26.6 to 27.0.1 was about 1 hour 15 minutes.

I have read online in various forums that one "trick" is to disable Bluetooth to try to force the watch to use WiFi only for this, which can be much faster. But I think the Bluetooth connection to the iPhone is needed here and I did not want to do anything different from what Apple instructs. So I just left it alone, watched Sunday football, and sure enough, it completed just fine.

Benjamin Franklin once said (240 years ago): "a watched pot never boils."

Corollary: "a watched update never finishes"

Other corollary: "a watched backup never finishes"

If you are watching the update as it downloads or proceeds, it will feel like it is taking forever. Find something else to do. And make sure you follow Apple's instructions exactly. This includes leaving the watch on its charger untouched, with at least 50% charge, during the update process, and the iPhone should be well charged also. If you have less than 50%, the update may pause or proceed very slowly. Another point: after my watch completed its lengthy download, it was waiting for me to click an "Install" button to proceed, but I did not realize that it was waiting for me, for a while. If you don't click that "Install" button, it literally will take forever.

Your other problem about Activity and heart rate not working ... those are likely related as Activity includes and depends on heart rate data. Heart rate can fail to be measured when

• Watch band and fit to arm/wrist is not adjusted quite right. Try tightening the band and centering the watch in the middle of the arm, and sliding it a few tenths of an inch up the arm away from the hand. Some experimentation may be needed here.
• Also, be sure to gently wipe/clean the sensor underside of the watch with a clean microfiber cloth after all exercise or exposure to any of sweat, sunscreen, soap, shampoo, chlorine, or any other chemicals. In fact it is best to avoid any exposure to soap, shampoo, sunscreen, etc.
• If in low power mode, heart rate measurements will be reduced or even skipped

Why the Update Takes So Long

• Resource Limits: Apple Watch updates route through Bluetooth and Wi-Fi simultaneously, and the watch has limited processing power to unpack and verify system files.
• Time Frames: An update routinely takes 45 minutes to over 2 hours.
• Safety Rules: The watch must stay on its charger with at least 50% battery and remain untouched so it does not abort or corrupt the installation. 

if the update is stuck downloading you might want to remove the update file and try the update again

Watch app on your iPhone > General > Storage, find the watchOS update file, delete it, and download it again.