I had the same problem when I got my watch. It was resolved with help user manual on the page 72.
Conditions for Storing Log Data in Memory> • The log number and log data are stored in memory when the watch remains at a depth of more than 1 m (4 ft) for 3 minutes or more, or it remains at a depth of more than 8 m (27 ft) for 1 minute or more.
Answers & Comments
I had the same problem when I got my watch. It was resolved with help user manual on the page 72.
Conditions for Storing Log Data in Memory>
• The log number and log data are stored in memory when
the watch remains at a depth of more than 1 m (4 ft) for
3 minutes or more, or it remains at a depth of more than
8 m (27 ft) for 1 minute or more.
It's not a bug it's feature :)