After the most recent firmware update to version 13.70, complete satellite dropouts started appearing on the Forerunner 945 watch. It happened seven times during yesterday's 2 hour ride with route loaded and once during today's one hour ride without route. I tried rebooting the watch between the rides, but that didn't eliminate the issue.
The only solution I could figure out was to press the Start/Stop button (and stop the activity), click "Resume Later", press the Start/Stop button, to get back to the activity, wait for GPS to acquire again and then resume the activity. No notification that satellite signal was lost appeared either, so many hundreds of meters of the record were lost before I noticed.
It's very very annoying. No such issues happened before the latest firmware update.