I'm not familiar with the M5's but did you check the fuel filter? Sounds like a clogged filter but could be other things and just a coincidence that it started after filling up.
I'm basically in the same situation with my 2016. When I first purchased it I had the first oil change at 3,500 miles then each one after at apprx. 1 year.
At 11 years next month it has 49,600 on the odo.
Makes sense. For me it wouldn't be a problem since I have all work done at the dealer, including tires and battery. My dealer is pretty good, reasonably priced and no up-sell.
It looks like I-Stop lives, they just made it harder to deactivate by burying in the menus. The salesman said the young hipsters like all the high-tech stuff.
Was at the dealer this morning for some routine maint. on my 19 Reserve. Dealer had a decent amount of 26's. Had the salesman open one on the lot so I could sit in it and play around with the controls. Still has CD. Not sure about I-Stop. The off button was not on the left of the steering wheel...
Has anyone actually looked at the interior of the 26's to see what can actually be controlled off the steering wheel? I've seen a few pictures that show alot of buttons on both sides of the steering wheel but can't see the detail.
I've have an appt. Thursday morning at Mazda dealer so I'll see...