Cantankerous curmudgeon
8
have you tried degaussing it?
It might be due to the watch being magnetized. It can happen from being too close to electro-magnetic sources and/or permenant magnets. Any watch AD can degauss it for you on the spot. My RG AP royal oak offshore was +1min /day. After my local AD degaussed it it was around +7sec/day.
PS try resting it on different positions at night to test for variances.