Have you tried a factory reset? Press and hold MENU, CLOCK, and UP simultaneously. Select YES when prompted.
If it's been 15 months, I'm wondering whether you have changed the battery?
Thanks to those that offered advice. I replaced the battery but it didn't fix the 'setting pool length' option. I did one master reset and the issue was resolved.
First battery replacement since I got the watch two years ago.
Similar symptoms -- no battery warning, but suddenly it won't sync or let me choose a pool size. After replacing the battery and no joy, I tried the factory reset -- same deal. No good. It says it has 'User Settings' to install, whatever that means, but it gives me a 'Transfer Error' to boot.
Anyone have the way to fix this?