Rolex gaining over an hour per day (?!)

[Holy_Peanuts]

Hi everyone.

I purchased an early 2000s Bluesy at auction several years ago. It was running fast (30 seconds per day) so I brought it to a local watchmaker to have it cleaned and open the caseback to ensure everything was kosher. He said everything looked good in terms of authenticity. If I remember correctly, the beat rate was very off and he made some minor adjustments and got it running at around +/-5 seconds per day.

Since then, the watch has been in storage. Took it out yesterday for a special occasion and noticed that it gained 44 minutes in 12 hours!

Thought the potential culprit was magnetization and found a website that claims that theres an app you can install on your phone (Physics Toolbox Magnometer) to use as a quick DIY to check for magnetism. The reading jumps dramatically when I bring the phone close to a speaker, but unfortunately, it doesn't change at all near the watch.

Any ideas what can be happening here? Looking like I'll be making my first trip to an RSC..