Watchbros srs (service/maintenance)

Omega SMP 2018. Ran +0.8sec a day consistently for years. Sold it to a guy who kept it for 2 years, bought it back... its running -6 a day.

Sign of a problem here or needing service? Maybe magnetism? Dunno if I should just send it off, but cba, since its not even up to the service window yet