It's probably just a higher rate of autonomous vehicles needing stop signs and buses identified at that moment, and cognitive bias causes you to only remember when that happens when you recently performed an update. /s
I can't tell whether you're serious but in case you are, this theory immediately falls apart when you realize waymo operates at night but there aren't any night photos.
I'm certain the User-Agent is part of it. I know that for certain because a very reliable way I can trigger the CF stuff is this plugin with the wrong browser selected [1].
[1] https://addons.mozilla.org/en-US/firefox/addon/uaswitcher/