Automatic updatesFirst contact with the Windows 10 was a laptop of my colleague. After the upgrade, 3G modem (WWAN) stopped working. The reason was an older modem firmware.
When the modem driver was returned to the older version, it worked until the next automatic update. After the boot-up the modem failed again.
The firmware update should have been updated before the Windows update. Although Microsoft's data collection and compatibility checks decreased computer's performance at every boot-up, there was no warning at all.
Anniversary updateAnother experience came just recently. A company's shared laptop was updated on an experimental basis in Windows 10. This computer did not have any particularly important role so, if necessary, it could be temporarily replaced with another one.
One morning we announced that the Windows update was going on. After some automatic reboots the screen was blank. After waiting time enough we forced the power off and restart the machine. It was a new experience for us to see a qr-code snippet as a part of blue screen.
Go back to the previous build of Windows.
After the restore, the machine was the pre-upgrade state. However, I was curious to see, how the upgrade occurs. This time I followed the progress of the upgrade. After a few auto-reboots the upgrade progress reached 99%. Then the screen went black. Now I let the laptop be powered several hours without success.
There were no other choices but power off. It was not a suprise to see the qr-code again. Installation media was ready, so this time the machine was operational in under an hour.