Do you trust the timing ap?
Suggest you check it against something else, I always use a quartz analogue watch or a website that I know is correct.
12.5 secs us a lot, it won’t take many days to verify it. Suggest check it morning and night, then leave it dial up overnight. That’ll tell you what it’s doing on the wrist and what its doing overnight. Wearing it to sleep introduces more variability.
A gain of this magnitude is disappointing and provided the watch is running well it could be addressed by regulation. Suggest you get more data as I’ve suggested to back up what you've seen. Here’s a silly question but I’ll ask it, did you alter / reset the watch to correct for different timezones during the holiday?